George Andrew Olah Across Conventional Lines

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GENERAL ARTICLE George Andrew Olah Across Conventional Lines

Ripudaman Malhotra, Thomas Mathew and G K Surya Prakash

Hungarian born American chemist, George Andrew Olah was aprolific researcher. The central theme of his career was the 12 pursuit of structure and mechanisms in chemistry, particu- larly focused on electron-deficient intermediates. He leaves behind a large body of work comprising almost 1500 papers and twenty books for the scientific community. Some selected works have been published in three aptly entitled volumes, 3 Across Conventional Lines. There is no way to capture the many contributions of Olah in a short essay. For this appreciation, we have chosen to high- 1 light some of those contributions that to our mind represent Ripudaman Malhotra, a student of Prof. Olah, is a asignificant advance to the state of knowledge. retired chemist who spent his entire career at SRI International working mostly Organofluorine Chemistry on energy-related issues. He co-authored the book on Early on in his career, while still in Hungary, Olah began studying global energy – A Cubic Mile organofluorine compounds. Olah’s interest in fluorinated com- of Oil. pounds was piqued by the theoretical ramifications of a strong 2 Thomas Mathew, a senior C-F bond. Thus, whereas chloromethanol immediately decom- scientist at the Loker Hydrocarbon Research poses into formaldehyde and HCl, he reasoned that the stronger Institute, has been a close C-F bond might render fluoromethanol stable. He succeeded in associate of Prof. Olah over preparing fluoromethanol by the reduction of ethyl flouorofor- two decades. 3 mate with lithium aluminum hydride [1]. He went on to pre- G K Surya Prakash – Chair, Department of Chemistry, pare a wide range of organofluorine compounds whose synthesis University of Southern required discovering new methods of synthesis, often requiring California and Director of the reagents, which are difficult to obtain such as hydrogen fluoride Loker Hydrocarbon Research Institute holds the Olah Nobel (HF), fluorosulfonic acid (FSO3H) and boron trifloride (BF3). Laureate Chair in Many of the organofluorine compounds that he prepared displayed Hydrocarbon Chemistry. He physiological activities and found applications as insecticides, fungi- has been a graduate student, cides, and therapeutics, which he investigated in collaboration close colleague, and friend of Prof. Olah over four decades.

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Scheme 1. Preparation of Freons by ﬂuoride exchange.

Keywords with his colleagues in the medical school in Hungary [2, 3]. Electron-deficient intermediates, Friedel–Crafts chemistry, carbo- Since early on, Olah has combined his fundamental research into cations, carbanions, methanol structure and mechanism with an eye on solving the problems economy, anthropogenic chemical facing the chemical industry. Finding practical solutions to these carbon cycle. problems was the main focus of his scientific research. Dur- ing this period, chlorofluorocarbons (CFCs, Freons) were impor- Since early on, Olah tant refrigerants known. They were produced by the reaction of combined his chlorocarbons with anhydrous HF catalyzed by aluminum chlo- fundamental research ride (AlCl ) or antimony pentafluoride (SbF ) and antimony tri- into structure and 3 5 mechanism with an eye fluoride (SbF3). In these reactions, Lewis acid such as AlCl3 on solving the problems co-ordinates with one of the lone pairs on the chlorine of the facing the chemical organochlorine compound and polarize the C-Cl bond render- industry. ing the carbon somewhat positively charged. This allows even − a weakly nucleophilic fluoride ion to displace the AlCl4 .The formation of a stronger C-F bond in place of a relatively weaker C-Cl bond being the driving force for the overall reaction. This ability of Lewis acids to enhance the reactivity of electrophiles was a major aspect of Olah’s research. The use of anhydrous HF presented several challenges to the industrial production of Freons, and Olah invented a continuous vapor phase process in which the chlorocarbons were contacted with pellets of fluoride salts, typically LiF or CaF2, in a porous bed while being irradiated with UV light (Scheme 1) [4].

Lack of access to basic chemicals such as anhydrous HF, FSO3H, and BF3 desperately needed for his research did not discourage him. He and his colleagues prepared HF from ﬂuorspar (CaF2)

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and sulfuric acid (H2SO4), and by reacting it with sulfur triox- ide (SO3) (generated from oleum) provided FSO3H. BF3 was obtained by treating boric acid (H3BO3) with FSO3H. An unex- pected present – a gift of a cylinder of boron trifluoride – from Hans Meerwein (University of Marburg, Germany) in the early fifties was indeed a wonderful gesture and help, for which Olah had always been grateful. Though Olah’s initial research work involved reactions of fluorinated carbohydrates, he became in- terested in Friedel–Crafts acylation and subsequently alkylation reactions with acyl and alkyl fluorides with boron trifluoride as a catalyst. This was the beginning of a long-standing interest in his pioneering work on electrophilic aromatic and aliphatic substitution reactions.

Friedel–Crafts Chemistry

The ability of AlCl3 in activating alkyl and acyl chlorides was well recognized since Friedel and Crafts had used it to produce alkyl and acyl benzenes. The addition of aromatic compounds to AlCl3 generally produces a deep red, dense oil forming π- complexes between the arene and AlCl3. No bond is formed between the AlCl3 and any speciﬁc carbon atom of the arene, and the arene retains most of its aromatic character. Most of the arene was not soluble in the red oil, but the addition of dry hydrochlo- ric acid (HCl) was known to render it soluble. In contrast, during Friedel–Crafts reactions, a σ-complex is formed between the alkyl or the acyl group and one of the carbon atoms. The resulting cyclohexadienyl carbocation is also known as the ‘Wheland intermediate’ (Scheme 2) [5, 6]. These intermediates are not aromatic, but the ion is somewhat stabilized by conjugation. The loss of a proton from the Wheland intermediate leads to the formation of the stable substituted arene.

Olah and his associates studied the use of BF3 to catalyze Friedel– Crafts reactions. Earlier investigators had attempted to use BF3 Olah and his associates with alkyl and acyl chlorides and bromides but were unsuccess- studied the use of BF3 to ful. Olah found that alkyl and acyl ﬂuorides could be activated catalyze Friedel–Crafts reactions.

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Scheme 2. Cyclohexadienyl carbocations (Wheland intermediates) formed during Friedel–Crafts reactions.

with BF3 to produce substituted aromatics (Scheme 3, (6), (7)). − − − The extraordinary stability of BF4 relative to BF3Cl or BF3Br was the principal reason why BF3 was an effective catalyst with acyl and alkyl fluorides. Indeed, Olah pioneered the use of fluorides with BF3 in Friedel–Crafts reactions. These reactions were much cleaner and did not produce the red oil, characteristic of reactions with AlCl3. Further investigations with BF3 catalysis, led to the discovery that silver tetrafluoroborate (AgBF4) could be used with alkyl or acyl chlorides to generate alkyl and acyl 1Simple exchange of cations tetrafluoroborates via metathesis1 (Scheme 3, (8), (9)) that then and anions between the react- could react with arenes to form the substitution products [7]. ing compounds in a reaction resulting in the formation of new An important contribution to our fundamental understanding of products: AB+CD → AD+BC. these reactions was the isolation of the σ-complexes of arenes with HF:BF3 [7, 8]. By itself, BF3 does not interact with methylbenzenes (toluene or xylene), nor is it very soluble in them in the temperature range −25 oCto−85 oC. Anhydrous HF also does not react with these aromatics at these temperatures and has limited solubility in them. However, when BF3 is added to a mixture of toluene or xylene and HF, it dissolves in the arene forming a greenish yellow equimolar complex of arene, HF, and BF3.Olah was able to isolate crystalline complexes from different methylbenzenes, determine their melting points, and show them to be the

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Scheme 3. Friedel–Crafts alkylation, acylation, and formation of carbocations. prototypical Wheland intermediates, [6] noticed during Friedel– Crafts reactions. What this finding demonstrated was that the conjugate acid, tetrafluoroboric acid (HBF4) was strong enough to protonate even a very weakly nucleophilic carbon of an aromatic hydrocarbon. Friedel–Crafts reactions found applications in the production of many industrial chemicals such as solvents, dyes and pharmaceu- ticals. Related to the Friedel–Crafts alkylation and acylation are a host of other electrophilic aromatic substitution reactions which proceed via a similar pathway, and thereby extend the application of Friedel–Crafts chemistry to a broad range of products. These include named reactions like Gattermann [9] and Gattermann– Koch [10] for the synthesis of aldehydes with hydrogen cyanide (HCN) or carbon monooxide (CO) respectively, as well as aromatic nitration and sulfonation reactions. In each of these reactions, a key step is the formation of a positively charged species, Related to the which adds to the aromatic ring forming a cyclohexadienyl car- Friedel–Crafts alkylation bocation – the Wheland intermediate. A loss of proton from this and acylation are a host of other electrophilic intermediate leads to the final product. aromatic substitution reactions which proceed via a similar pathway, Aromatic Nitration and thereby extend the application of The contributions of Olah to the field of aromatic nitration can be Friedel–Crafts chemistry best appreciated after a brief review of what was known about to a broad range of products.

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these reactions. Aromatic hydrocarbons are readily converted The Hughes–Ingold into their nitro derivatives by concentrated nitric acid (HNO3) mechanism for nitration itself or in other strong acids like sulfuric or phosphoric acid involves the generation (H PO ) with stoichiometric amounts of nitric acid. Studies by of nitronium cation 3 4 followed by its Hughes, Ingold, and others in mixed acids, mainly sulfuric acid subsequent electrophilic helped elucidate the mechanism of the reactions consisting of sev- substitution to an eral steps. aromatic center. The Hughes–Ingold mechanism for nitration involves the gener- + ation of nitronium (NO2 ) cation followed by its subsequent electrophilic substitution to an aromatic center (Scheme 4) [11]. The nitronium cation is usually generated in situ by the use of either neat nitric acid or by adding a second, stronger acid to help ac- celerate the generation of nitronium cation. The classic two-acid system called the nitrating mixture has, for decades, been a mixture of nitric acid as the nitrating agent and concentrated sulfuric acid as the acid catalyst. Several other acids have been used in the place of sulfuric acid. These include aluminum chloride, polyphosphoric acid, perchloric acid, methanesulfonic acid, hydrogen fluoride, and even superacids such as boron trifluoride, triflic acid, fluorosulfonic acid, etc. The first two steps involve the acid catalyzed transformation of + nitric acid into nitronium ion, NO2 , which was identified as the de facto nitrating agent. If steps (III) or (IV) (Scheme 4) were the rate-determining step, this mechanism could explain the observed first-order dependence of the rate in nitric acid and the arene. The reaction rates were known to increase dramatically with the increasing strength of sulfuric acid, which governed the + equilibrium concentration of NO2 relative to other two species – nitric acid and anion A−. The rates leveled off above about 95% sulfuric acid by which point nearly 100% of the added nitric acid + was converted to NO2 , the nitrating species. The Ingold mechanism readily accounted the effects of substituents on the reactivity and the isomer distribution of product nitroarenes. Through their inductive effect, electron-donating groups on the benzene ring increase its reactivity, and conversely, electron- withdrawing groups reduce the reactivity. Electron-donating sub-

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Scheme 4. Hughes-Ingold mechanism of electrophilic aromatic nitration. stituents typically direct the incoming nitro group to positions ortho (o-)orpara (p-) to them. This result is in keeping with the increased electron density at the ortho- and para- positions in the arene with electron-donating substituents. Electron-withdrawing substituents, on the other hand, preferentially reduce electron density at the o- and p- positions, and consequently direct the incoming nitro group to the meta (m-) position, which relatively has a higher electron density. Apart from their inductive eﬀects, the substituents can also stabilize the intermediate via resonance effects. Thus, chlorobenzene which is less reactive than benzene nevertheless directs the incoming nitro group to the o- and p- positions because the Wheland intermediates for those positions can be stabilized by conjugation with chlorine (back bonding with chlorine lone pair). Previous work had shown that nitration of aromatics could also be achieved by treating them with nitryl chloride (NO2Cl) in the presence of AlCl3 [12]. Some nitration had also been observed with nitryl ﬂuoride (NO2F). However, the reaction with deactivated aromatics such as halobenzenes was not successful. Olah

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Scheme 5. Nitronium tertaﬂuoroborate, an eﬃcient nitrating agent.

had synthesized stable complexes of nitryl fluoride with BF3, and + found that it could dissociate to give NO2 in polar solvents. His studies revealed that nitronium tetrafluoroborate (NO2BF4)isa very effective nitrating agent [13]. Olah prepared it initially from HNO3,HFandBF3 in a simple and efficient way (Scheme 5). Analogous to acylation reactions, Olah and co-workers investigated aromatic nitrations by NO2Cl in the presence of AgBF4. They expected metathesis reaction between both to produce NO2BF4 along with precipitation of silver chloride (AgCl). They found this combination to be extremely effective and could prepare nitro derivatives from even deactivated aromatics including halobenzenes and benzotrifluoride (C6H5CF3) [14]. They further showed that aromatics could be nitrated with them in non-acidic media such as nitromethane (CH3NO2) or sulfolane (C4H8O2S). The reactions with preformed NO2BF4 were extremely fast and applicable to a wide range of aromatic substrates, including the strongly deactivated substrates like nitrobenzene (C6H5NO2) and benzonitrile (C6H5CN) [14]. The fast reaction rates precluded measurement of kinetics, and Olah employed the technique of competitive nitrations to determine relative reactivity of different arenes. Significantly, whereas toluene (C6H5CH3) was typically about 20 times more reactive

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than benzene (C6H6) in acid-catalyzed reactions, with preformed nitronium salts, the relative reactivity was significantly reduced to around 1.5. The low substrate selectivity suggests that nitration Olah invoked the idea occurs at nearly every encounter between the nitronium ion, ben- that the substrate zene, and toluene. Yet, high positional selectivity of nitration of selectivity was determined during the toluene was observed with most of the nitration occurring at sites formation of a ortho and para to the methyl group while m-nitration was only π-complex between the about 2%. To some extent, incomplete mixing between the arenes arene and the nitronium and nitronium salt could have contributed to the observed low ion, while the positional selectivity was substrate selectivity. However, high positional selectivity along determined during the with low substrate selectivity was also noted for arenes more re- conversion of the π active than toluene, such as anisole (C6H5OCH3) and naphthalene -complex to the σ (C H ), whose kinetics suggested reactions at encounter rates. -complex, the Wheland 10 8 intermediate. Olah resolved this conundrum by introducing the idea that the positional and substrate selectivities were determined in separate transition states. He invoked the idea that the substrate selectivity was determined during the formation of a π-complex between the arene and the nitronium ion, while the positional selectivity was determined during the conversion of the π-complex to the σ- complex, the Wheland intermediate [6,14]. This was a significant modification to the Ingold mechanism, and it stimulated further research by others. While agreeing with Olah on the need for a second step, other researchers have debated over the nature of the first intermediate. Ridd introduced the concept of an encounter complex in which the nitronium ion and the arene were held together in a solvent cage while there were no specific intermediate species prior to the Wheland intermediate [15]. At the other end, Perrin considered a complete electron transfer from the arene to the nitronium salt for aromatics more reactive than toluene [16].

Carbocations

The Hungarian Uprising in October 1956, followed by the So- viet invasion in November, compelled Olah to leave Hungary and move to the West [17]. In 1957, he joined the exploratory laboratory of Dow Chemicals at Sarnia, Ontario, and continued his

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investigations into Friedel–Crafts reactions using Lewis acids like BF3 and SbF5 with alkyl and acyl fluorides. Dow Chemical Com- pany was a major user of Friedel–Crafts chemistry to produce ethyl benzene (C6H5C2H5), precursor of styrene (C8H8) for the synthesis of polystyrene. Olah investigated these reactions of industrial importance while also continuing his research into the fundamentals of the underlying chemistry, specifically on the nature of the carbocations. Studies by Ingold and Hughes, and later by Whitmore had led to the recognition of carbocations as key reactive intermediates, in many reactions like eliminations proceeding via the E1 mechanism, or substitutions proceeding via SN1 mechanism. While carbocations had been implicated in these reactions, they had never been observed. The lack of their observation was attributed at that time to the inherent instability of positively charged carbon species, and many leading chemists doubted their existence as ‘intermediates’ [18]. Alkylations with primary alkyl chlorides led to products in which the alkyl group had undergone rearrangement. Thus, alkylation of benzene with n-propyl chloride produced cumene (isopropylben- zene). Such rearrangements were characteristic of reactions that proceeded via carbocations; here the driving force was the formation of a more stable secondary carbocation from the primary ion. Similarly, acylation of aromatics with pivaloyl chloride also led to some t-butylation, presumably by the t-butyl cation, which was produced by decarbonylation of the intermediate pivaloyl cation, + (CH3)3CCO [19]. Olah reasoned that the chief reason for their fleeting existence was the nucleophilicity of the medium. Accordingly, he sought ways to extend their lifetimes to permit their observation and study by focusing on unconventional solvents such as liquid SO2 and liquid SO2ClF, which have sufficient polarity (high dielectric con- stants) to dissolve ions but are poor nucleophiles. To suppress the reactivity of the counter ion, often a halide, he used Lewis acids such as SbF5 or BF3 to bind with them and generate stable anions − − − like SbF6 ,Sb2F11 or BF4 (Scheme 6) [20, 21]. Previously, he

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Scheme 6. Formation of carbocations from alkyl/acyl fluoride using strong Lewis acid SbF5 by binding the anion. had used conductivity measurements to demonstrate that in polar solvents, the donor-acceptor complexes between the fluoride and the Lewis acid dissociate into distinct ions. However, presence of moisture in the medium, even in very small amounts, could lead to ionized HF resulting in an erroneously higher electrical conductivity. In the US, Olah had access to various spectroscopic tools to study the structure of the resulting species. IR spectra of 1:1 complexes of acyl fluorides with SbF5 tellingly showed no absorption band due to the C–F bond, but showed bands around 2280 cm−1 corresponding to the carboxonium ion, RC≡O+ [21]. In these carboxonium ions (acylium ions), most of the positive charge is on the oxygen, although the carbon atom also bears some of the positive charge.

Olah pioneered the use of nuclear magnetic resonance spectroscopy Olah pioneered the use for the study of carbocations [21]. Low-temperature proton, 19F, of nuclear magnetic and 13C NMR spectra of a series of acyl fluorides and their 1:1 resonance spectroscopy for the study of complexes with SbF5 were recorded in liquid SO2ClF or SO2. carbocations. Whereas 1H NMR of the acyl fluorides showed the characteristic 1H−19F splitting, the complexes did not show any splitting. This result is consistent with the dissociation of the complexes into − the carboxonium ion and the SbF6 , although a rapid exchange of fluorine in the polar solvent could also wash out any splitting.

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Another characteristic of the spectra was the significant deshield- ing of the proton NMR resonances of the acyl moieties resulting from the positive charge. In the case of neat pivaloyl fluoride, the methyl resonance occurs at 1.27 ppm (relative to tetramethylsi- lane). The spectrum with added SbF5 in SO2 showed three distinct resonances at 1.35, 2.02, and 3.95 ppm. The 1.35 ppm resonance was assigned to the (CH3)3CCOF:SbF5 complex, while the + line at 2.02 ppm was assigned to the acylium ion, (CH3)3CCO [19, 21]. An approximately 1.5 ppm shift was consistent with other cases where the methyl was one carbon away from the carboxonium center. The strongly deshielded resonance at 3.95 ppm was suggestive of a methyl directly attached to a positive center, possibly the t-butyl cation formed by the decarbonylation of the pivaloyl ion. Decarbonylation had also been observed during attempts to prepare the pivaloyl carboxonium hexafluoroanti- monate salt for IR studies. The t-butyl cation was the first long- lived alkyl carbocation to be observed [19–23]. The structure was confirmed by recording the spectrum of t-butyl fluoride with excess SbF5 in SO2, which showed a single resonance at 4.35 ppm [20]. Analogously, the isopropyl cation was produced. This cation has a proton on the charge bearing carbon, and its 1HNMR shows a highly deshielded septet at 13.5 ppm. The splitting pat- tern confirms that the proton on the central carbon was not en- gaged in any rapid exchange with the medium, and all the six methyl protons were coupled to it. Subsequent studies on 13C NMR spectra of the t-butyl cation showed methyl peaks at 47.5 ppm and a single highly deshielded carbon at 335 ppm, shift of more than 300 ppm from the parent fluoride [20]! For reference, methyl carboxonium (acetylium) peak was roughly 45 ppm downfield from the parent acetyl fluoride carbonyl peak [19–22]. Alkyl cations can be Alkyl cations can be produced by several pathways including produced by several pathways including acid-catalyzed dehydration of alcohols and addition of proton to acid-catalyzed olefins. Previous attempts at observing alkyl carbocationic species dehydration of alcohols by the reaction of alcohols or olefins with strong acids like sul- and addition of proton to furic or perchloric acid had not been successful. Evidently, in olefins.

1122 RESONANCE | December 2017 GENERAL ARTICLE these acids, the carbocation can lose a proton to produce an oleﬁn, which can then engage in addition, cyclization, or polymerization reactions with other carbocations. What was needed was an even stronger acid – a superacid – to suppress the deprotonation of the alkyl cations. Although the term superacids was coined by Co- nant [24] in the 1920s to refer to very strong acids, it was Gille- spie who gave it a quantitative thermodynamic basis. The term applied to acids stronger than 100% sulfuric acid, or those with a Hammett acidity function, H0, of less than -12 [25].

Following his successful formation of stable t-butyl cation in SbF5, Olah’s group proceeded to examine the use of fluorosulfuric acid (FSO3H) in conjunction with SbF5. Combination of Brønsted acids with Lewis acids was known to enhance the acidity [26]. In a collaboration with Gillespie, Olah found that a variety of alkyl carbocations can be produced with the FSO3H/ SbF5 mixtures from not only the abstraction of a fluoride anion from alkyl fluorides but also by the protonation of olefins or protonation of alcohols followed by dehydration [27]. These early studies on carbocations led Olah to make an important distinction between trivalent carbenium ions, which have two-center two electron bonds, and tetra- or penta- co-ordinated carbonium ions, which have a three-center two-electron bond [28]. The prototype of a nonclassical ion is trihydrogen cation (proto- + nated molecular hydrogen, H3 ), formed by the addition of a proton that bridges the sigma bond in H2. It is a stable structure commonly observed in the gas phase. It is noteworthy that it is one of the most abundant ions in the universe, stable in the interstellar medium (ISM) due to the low temperature and low density of interstellar space [29]. Analogously, a proton or a carbenium ion may bridge a C–H or a C–C sigma bond producing stable nonclassical carbonium ions. Therefore, protonation of xenon or methane can be envisaged as it does not violate the octet rule. A bonding electron pair (responsible for covalent bonding between C and H atoms) or a non-bonding lone pair is forced into sharing with the proton, resulting in 2-electron 3-center bonding + (2e–3c) to give protonated methane (methonium, CH5 ) and pro-

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Figure 1. Nonclassical ions as discrete example of hypercoordination.

tonated xenon (XeH+). Higher alkanes are protonated similarly. + Recently, Ali et al., reported the presence of CH5 ) in the upper atmosphere of Titan (moon of Saturn.) from the data obtained from the onboard mass spectrometer in the Cassini spacecraft [30]. In 1962, Olah presented his ﬁndings on the observation of stable carbocations in superacids at the Brookhaven Organic Reaction Mechanisms Conference [31]. The conference featured an ongoing debate between Winstein and Brown on the nature of the 2- norbornyl cation. Solvolysis rates of exo-2-norbornyl esters were substantially faster than the corresponding endo-isomers. Both isomers selectively gave the exo- product from the solvolysis [32]. These observations had led Winstein to propose a ‘neighboring group’ participation by the C1–C6 single bond in the intermediate 2-norbornyl cation. Enhancement of solvolysis rates by neighboring group participation through π-bond was well recognized, for example, in the solvolysis of phenethyl bromide via formation of the phenonium ion. But, the idea of a σ-bond participation in this manner met with great resistance. The direct observation of carbocations using low-temperature NMR spearheaded by Olah and co-workers, and his Brookhaven Conference presentation, oﬀered a great opportunity to probe the structure of the 2-norbornyl ion thrusting him into the nonclassical- classical ion controversy. Olah began an investigation of 2-norbornyl

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Scheme 7. Formation of 2-norbornyl cation from three different precursors. and related cations. The production of these ions turned out to be quite straightforward; they could be generated by treating 2- norbornyl fluoride or cyclopentenylethyl fluoride with SbF5,or by the protonation of nortricylene with FSO3H/SbF5. In fact, the major product of elimination reaction of 2-norbornyl ion is nor- tricyclene (Scheme 7) [33]. At room temperature, the mixture of 2-norbornyl fluoride and SbF5 showed a single resonance for all the protons. This result points to the facile 1, 2-hydride shifts and the Wagner–Meerwein rearrangement which render all the protons equivalent. When the o SO2ClF solution was cooled to -78 C and the spectrum recorded at this temperature, it showed three resonances with integrated intensities of 6:1:3 corresponding to a structure in which the hydride shift had been frozen out, but not the Wagner–Meerwein rearrangement product. Proton and carbon (13C enriched) NMR spectra of the solutions cooled down to -159 oC showed spectra consistent with the symmetric bridged nonclassical structure. In To resolve the question o SO2ClF at -78 C, the spectra were consistent with either a sym- of rapidly equilibrating metric structure, as nonclassical ion, or a pair of rapidly equili- ions versus a bridged ion, Olah collaborated brating classical ions. The inability to freeze out the equilibrating with Mateescu to probe ions at this temperature meant that the barrier, if any, between the the structure of various two species, was less than 8 kJ/mol [34–37]. carbocations with core electron spectroscopy.

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To resolve the question of rapidly equilibrating ions versus a bridged ion, Olah collaborated with Mateescu to probe the structure of various carbocations with core electron spectroscopy2 [38]. Many dynamic processes such as rapid intramolecular rearrangements can occur many times on NMR time scale. ESCA, on the other hand, probes structures on a time scale much shorter than even a 2Electron spectroscopy for single vibration and thus see the structure of individual structures chemical analysis, ESCA. in a rapidly equilibrating system. Carbon 1-s ESCA spectra for the t-butyl ion and the 2-norbornyl ions were recorded at low temperature in frozen matrices of SbF5. In the classical t-butyl carbenium ion, the binding energy difference between the core electrons of the positively charged carbon center and the methyl carbons was about 4 eV. In contrast, the spectrum of the 2-norbornyl cation showed a broad peak with a shoulder at barely 1 eV higher binding than the one for the rest of the carbons. This result was a further evidence for the bridged carbonium ion structure as originally proposed by Winstein. A final confirmation of the nonclassical structure was obtained by recording the spectrum of the ion at 5 K using solid-state NMR cross-polarization magic angle spinning (CPMAS) technique [39]. The inability to freeze out equilibrating structures at these cryogenic temperatures implies a barrier of less than 0.8 kJ/mol. After decades of extensive debate over the structural characteristics of 2-norbornyl cation (whether classical or nonclassical), very recently, Scholz et al., successfully isolated the pentacoordinated (nonclassical) 2-norbornyl cation as its solvated + − salt [C7H11] [Al2Br7] .CH2Br2 and structure of the bridged, non- + classical geometry of norbornyl cation [C7H11] , has been established by x-ray crystallographic analysis as the long-sought un- equivocal proof (Figure 2) [40]. Direct observation of stable, long-lived carbocations led to the recognition of the general concept of hydrocarbon cations, including the realization that five (and higher) coordinate carbocations are the key to electrophilic reactions at single bonds in saturated hydrocarbons (alkanes, cycloalkanes). Later, Olah with his colleagues showed by theory that the parent six-coordinate

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Figure 2. Three well- resolved crystallographi- cally independent nonclassical cation moieties I-III of 2-norbornyl cation at 40 K (Scholz et al.[40]).

2+ diprotonated methane (CH6 ) [41], which has two 2e–3c bonding interactions in its minimum-energy structure (C2ν) and the 3+ heptacoordinate triprotonated methane (CH7 ) [42], which has three 2e–3c bonding interactions in its minimum-energy structure (C3ν) are realistic. Schmidbauer has isolated the penta and hexacoordinated methanium salts with the replacement of hydrogen with organogold species, (Ph3PAu). Aurophilic interactions have signiﬁcant contribution in stabilization of these carbidoclus- + 2+ tures [(Ph3PAu)5C] and [(Ph3PAu)6C] (Figure 3, (a) and (b)) [43, 44]. These results indicate the general importance of 2e– 3c bonding in protonated alkanes. Hogeveen prepared the nonclassical pentagonal–pyramidal dication of hexamethylbenzene in 1973, at low temperatures in Magic Acid (FSO3H/SbF5) and he proposed a nonclassical structure with a hexacoordinated carbon based on NMR spectroscopy and reactivity studies (Figure 3, (c)) 2+ [45]. Recently, the crystal structure of [C6(CH3)6] isolated as

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Figure 3. Penta, hexa, and heptacoordinate parent methanium ions; Ph3PAu substituted methanium mono and dications (A and B); pentagonal-pyramidal dication of hexamethylbenzene (C- predicted structure and D- crystal structure by Malischewski and Seppelt [46]).

2+ − [C6(CH3)6] (SbF6 )2.FSO3H was determined by Malischewski and Seppelt as the predicted nonclassical pentagonal–pyramidal dication (Figure 3, (d)) [46]. In 1972, Olah suggested the name ‘carbocations’ for all the cations of carbon compounds, because the negative ions are called ‘carbanions’. He offered a general definition of carbocations based on the realization that two distinct classes of carbocations exist [47]. Trivalent (‘classical’) carbenium ions contain an sp2-hybridized electron deficient carbon atom, which tends to be planar in the ab- sence of constraining skeletal rigidity or steric interference. The carbenium carbon contains six valence electrons; thus, it is highly

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Figure 4. The two distinct classes of carbocations: carbenium and carbonium ions.

electron deficient. The structure of trivalent carbocations can always be adequately described using only two-electron two-center + bonds (Lewis valence bond structures). CH3 is the parent for trivalent ions. As mentioned (vide supra), penta- (or higher) coordinate (‘nonclassical’) carbonium ions contain five, six or seven (higher) coordinate carbon atoms. They cannot be described by two-electron two-center single bonds alone but also necessitate the use of two- electron three (or multi)-center bonding. The carbocation center always has eight valence electrons. But overall, the carbonium ions are electron deficient because of the sharing of two electrons + between three (or more) atoms. CH5 can be considered the parent for carbonium ions (Figure 4). Continued efforts led to the characterization of a vast library of carbocations – monoprotonated, diprotonated, triprotonated, tetra- protonated and so on. A few examples are shown in Figure 5.

Superacids

As already mentioned, the name ‘superacid’ was coined by J B Conant of Harvard in 1927 [24] to denote acids such as perchloric acid (HClO4), which he found to be stronger than conventional mineral acids and capable of protonating weak bases such as carbonyl compounds. Later, in the 1960s, Gillespie suggested this term for protic acids stronger than 100% sulfuric acid, a deﬁni-

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Figure 5. A few examples of carbocations and onium ions prepared and studied by Olah and co-workers.

tion that is now generally accepted [25]. Generally, the acidity of aqueous acids is expressed by their pH – the logarithmic scale of the hydrogen ion concentration (hydrogen ion activity). Acidity can be related to the degree of transformation of a base to its conjugate acid (this, in fact, will de- pend on the base itself). The so-called Hammett acidity function H0 relates to the half protonation equilibrium of suitable weak bases. The Hammett acidity function is also a logarithmic scale on which 100% sulfuric acid has a value of H0 = -12. The acidity of sulfuric acid can be increased by the addition of SO3 (oleum). Acids with H0 ≤−12 are designated as superacids. Perchloric acid (HClO4, H0 = -13.0), fluorosulfuric acid (FSO3H, H0 = - 15.1), and trifluoromethanesulfonic acid (CF3SO3H; H0 = 14.1) as well as 100% anhydrous hydrogen fluoride are considered to be superacids [26]. Complexing with Lewis acidic metal fluorides of higher valence, such as antimony, tantalum, or niobium pentafluoride, greatly enhances the acidity of these systems. In a generalized sense, acids are electron acceptors. They in-

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Scheme 8. Conjugate superacids from Brønsted acids with Lewis acids. clude both protic (Brønsted) acid and Lewis acids such as AlCl3 and BF3 that have an electron-deficient central atom. Conse- quently, there is a priori no difference between Brønsted (protic) and Lewis acids. In extending the concept of superacidity to Lewis acid halides, Olah suggested that those stronger than anhydrous AlCl3 (the most commonly used Friedel–Crafts acid) to be considered super Lewis acids. These superacidic Lewis acids include higher-valence fluorides such as antimony, arsenic, tantalum, niobium, and bismuth pentafluorides. Superacidity encom- passes both very strong Brønsted and Lewis acids and their conjugate acid systems. Friedel–Crafts Lewis acid halides form with proton donors such as H2O, HCl, and HF, conjugate acids such as H2O-BF3,HCl- + − + − 3 AlCl3, and HF-BF3, which ionize to H3O BF3OH ,H2Cl AlCl4 , The name was coined by J + − Lukas, a German post doctoral and H2F BF4 , etc., (Scheme 8). These conjugate Friedel–Crafts fellow working with Prof. Olah acids have H0 values less than -15. Thus, they are much stronger in the 1960s. Following a lab- than the usual mineral acids. Even stronger superacid systems are oratory Christmas party, he put 3 FSO3H-SbF5 (Magic Acid ), HF-SbF5 (fluoroantimonic acid), the remnants of wax candles into the acid. The wax dis- or CF3SO3H-B(O3SCF3)3 (triflatoboric acid). The acidity of an- solved, and the resultant solu- hydrous HF, FSO3H, or CF3SO3H increases by many orders of tiongaveanNMRspectrumof magnitude upon addition of Lewis acid fluorides such as SbF5, t-butyl cation evoking a sense which form large complex fluoroanions facilitating the dispersion of magic in the young scientist of the negative charge [26]. [18].

On addition of SbF5, the acidity function of FSO3H increases

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and it reaches -23.0 with equimolar amount of SbF5, the acidity of Magic Acid (1:1 FSO3H-SbF5). Fluoroantimonic acid is even stronger; with 4 mol% SbF5,theH0 value for HF-SbF5 is already -21.0 – 1000 times stronger than the value for ﬂuorosul- furic acid with the same SbF5 concentration. The acidity of the 1:1 HF-SbF5 system or those with even higher SbF5 concentra- tions reaches H0 ≈−28. Thus, these superacidic systems can be 1016 times stronger than 100% sulfuric acid!

Related superacid systems in which SbF5 is replaced by AsF5, TaF5,NbF5, etc., are of somewhat lower acidity but are still extremely strong acids. So is HF-BF3 – a very useful superacid that will not cause oxidative side reactions. Ternary superacid systems including, for example, FSO3H-HF or CF3SO3H-HF with Lewis acid fluorides are also known and used. The high acidity of superacids makes them extremely effective protonating agents and catalysts. They can activate a wide variety of extremely weakly basic compounds (nucleophiles) that previously could not be considered reactive in any practical manner. Superacids such as fluoroantimonic (HF-SbF5) or Magic Acid (FSO3H-SbF5) are capable of protonating not only π-donor systems (aromatics, olefins, and acetylenes) but also what is called σ-donors, such as saturated hydrocarbons including CH4 –the simplest parent saturated hydrocarbon as discussed (vide supra). The protonation of some π-, σ-, and n-bases and their subsequent ionization to their corresponding carbocations or onium ions are depicted in Figure 6 [48]. As expected, superacids were found to be extremely effective in bringing about protolytic transformations and other reactions of hydrocarbons. ‘Isomerization’ (rearrangement) of hydrocarbons is of substantial practical importance. Straight-chain alkanes obtained from petroleum oil generally have poorer combustion properties (expressed as low octane numbers of gasoline) than their branched isomers, hence there is a need to convert them into the higher- octane branched isomers [49–53]. Isomerizations are generally

1132 RESONANCE | December 2017 GENERAL ARTICLE

Figure 6. Protonation and subsequent ionization of π-, σ-andn-bases by the su-

peracid FSO3H-SbF5 or HF-

SbF5.

carried out under thermodynamically controlled conditions which lead to equilibria. As a rule, these equilibria favor increased amounts of the higher-octane branched isomers at lower temperatures [52]. Conventional acid-catalyzed isomerization of alkanes is carried out with various catalyst systems at temperatures of Alkylation combines 150–200 oC. Superacid-catalyzed reactions can be carried out at lower-molecular-weight much lower temperatures (even at or below room temperature), saturated and unsaturated and thus they give increased amounts of preferred branched iso- hydrocarbons to produce mers. This, together with alkylation, is of particular importance high-octane gasoline and in the manufacture of lead-free high-octane gasoline. These pro- other hydrocarbon cesses have been studied by Olah and co-workers extensively products. [53]. As mentioned, alkylation combines lower-molecular-weight saturated and unsaturated hydrocarbons (alkanes and alkenes) to produce high-octane gasoline and other hydrocarbon products. Con- ventional paraﬃn-oleﬁn (alkane-alkene) alkylation is an acid- catalyzed reaction, such as combining isobutylene and isobutane to form 2, 2, 4-trimethylpentane (isooctane). Carbocations play a key role in this and also in processes such as acid-catalyzed polymerization of alkenes, polycondensation of arenes as well as

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in the ring opening polymerization of cyclic ethers, sulﬁdes, and nitrogen compounds. Superacidic oxidative condensation of alkanes can even be achieved, including that of CH4, as known with the co-condensation of alkanes and alkenes [54].

The combination of FSO3H and SbF5 (Magic Acid) was strong enough to protonate hydrocarbons causing them to undergo isomerization and β-scission reactions. It could even protonate CH4 + to give CH5 . Insertion of a proton in one of the C-H bonds of CH4 gives rise to this species. In turn, it can reversibly eliminate + H2 to produce CH3 . In the presence of D2 gas, Magic Acid can produce variously deuterated CH4 by a series of H-D exchanges [53]. The isomerization of alkanes by treatment with superacids found applications in petroleum industry for upgrading gasoline, con- verting natural gas to gasoline, or upgrading heavy hydrocarbons to distillate fuels. Branched alkanes have a higher octane than the corresponding normal alkanes. Furthermore, the molar volume of iso-alkanes is greater than the corresponding n-alkanes. Since gasoline is sold by volume, isomerization of the naphtha stream not only produces a more desirable product (higher octane), it also produces more of it. Olah developed various metal and metal-oxide supported superacid catalysts, efficient to carry out these reactions [55]. The formation of carbocationic species with superacids makes it possible to use them to effect Friedel–Crafts and associated reactions. In some instances, though, the use of very strong acids leads to some interesting results. Nitration of benzene in sulfuric acid or oleum produces nitrobenzene, which then undergoes further nitration to give di- and tri-nitro derivatives. In superacids, Treatment of coal with nitrobenzene is the sole product; the initially formed nitroben- 30% aqueous H2O2 and zene gets completely protonated and thus is rendered unreactive trifluoroacetic acid towards further nitration [56]. dissolves coal to give colorless solution Electrophilic oxygenation of arenes with hydrogen peroxide containing aliphatic (H O ) presents an interesting example. 100% Sulfuric acid can carboxylic acids. 2 2 protonate hydrogen peroxide or peracetic acid to form an elec-

1134 RESONANCE | December 2017 GENERAL ARTICLE trophilic oxygen carrier. Friedel–Crafts type reaction of this oxy- genating agent with benzene produces phenol, but because the product is much more susceptible to electrophilic substitution than benzene, the reaction proceeds further ultimately to produce CO and CO2. With toluene, the product is acetic acid. Deno ex- ploited this propensity for the oxidative destruction of aromatic moieties in the structural analyses of aliphatic portions of coal [57]. The structure of coal comprises a network of aromatic nu- clei crosslinked by aliphatic bridges. Treatment of coal with 30% aqueous H2O2 and triﬂuoroacetic acid (TFA) dissolved coal to give colorless solutions containing aliphatic carboxylic acids. On the other hand, during such oxidations in superacids, the product phenol being relatively basic, gets protonated and is thus protected from further oxidation/hydroxylation. The reaction with benzene or toluene proceeds cleanly to give phenol or cresol in superacidic media [58].

Amine-HF Ionic Liquids/Ionic Solids [(Onium Poly(Hydrogen Fluorides)]

Liquid hydrogen fluoride or sulfuric acid were used as catalysts for alkylation of isobutane with various alkenes in the major alkylation plants [59–61]. Due to serious environmental and safety risks associated with these catalysts, extensive efforts have been made to modify the existing processes and to develop a suitable liquid or solid catalyst, which is environmentally more benign and stable [62]. A good and efficient catalyst substitute for acids in paraffinic hydrocarbon isomerization and alkylation has been well sought HF to give pyridinium poly(hydrogen flu- Olah found that pyridine oride) (PPHF, complex with 30% pyridine and 70% HF known forms remarkably stable as Olah’s reagent) over the past few decades and many devel- solutions with anhydrous HF to give pyridinium opments have been made. Olah found that complexation of HF poly(hydrogen fluoride) with amines can reduce its volatility at room temperature signif- (PPHF, complex with icantly, making it a safer and more convenient catalyst system 30% pyridine and 70% for isoparaffin-olefin alkylation (Scheme 9). Olah also found that HF known as Olah’s reagent). pyridine forms remarkably stable solutions with anhydrous [63].

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Scheme 9. Formation of stable Amine-HF complexes. This complex has been found to be a very efficient organic flu- orinating agent. Olah and co-workers found that hydrogen fluoride, gives poly(hydrogen fluoride) with not only pyridine or picoline but with many alkyl and arylamines, their derivatives and polymers such as poly(ethylenimine) (PEI) and poly(4-vinyl pyridine) (PVP) [64]. The ionic liquids containing up to 70% by weight of HF, formed from pyridine, picoline, triethylamine, or triethanolamine give stable solutions and do not loose HF notice- ably when warmed up to 50 oC. With 2% crosslinked poly(4-vinyl pyridine), complexation results in PVPHF ionic solid, a solid equivalent of PPHF. These modified poly(hydrogen fluoride) ionic liquids and solids have helped alleviate the volatility and toxicity of anhydrous HF to a great extent. Isobutane-isobutylene/2-butene alkylation using pyridinium poly(hydrogen fluoride) (PPHF) as a catalyst showed that this system is a very efficient, convenient, and environmentally benign acid catalyst for alkylation process for high-octane alkylates (Alkad process by Texaco) [65]. In the case of an ac-

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Scheme 10. Alkylation of isobutane with isobutylene, major synthetic process in petroleum reﬁning. cidental release to the atmosphere, toxic aerosol cloud formation is greatly reduced or diminished (up to 95%) and the acid can be easily neutralized. This liquid complex can be considered as an ideal ionic liquid medium as well as an active acid catalyst for alkylation.

Naﬁon-H and Other Solid Superacids

Acids are not limited to liquid (or gaseous) systems. Solid acids also play a significant role. Acidic oxides such as silica, silica- alumina, and zeolitic substances are used extensively as solid acid catalysts. New solid acid systems that are stronger than those used conventionally are frequently called solid superacids. As applications of liquid superacids gained importance, efforts were directed towards finding solid or supported superacids suitable as catalysts. There are considerable difficulties in achieving this goal. For example, BF3 cannot be well supported on solids because of its high volatility making its desorption inevitable. SbF5,TaF5, and NbF5 have much lower vapor pressures and are thus much more adaptable to being supported or attached to solids. Because of their high chemical reactivity, SbF5, HF-SbF5, FSO3H- SbF5, etc., are preferentially supported on fluoridated alumina or fluorinated graphite. Solid superacids based on TaF5 or NbF5 are more stable than those based on SbF5 because of their higher resistance to reduction. Solid perfluorinated resinsulfonic acid catalysts, such as those based on the acid form of DuPont’s Nafion

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Scheme 11. Nafion-H catalyzed synthetic transformations. ionomer membrane resin, and some higher perfluoroalkanesul- fonic acids, such as perfluorodecanesulfonic acid, have gained use as solid superacid catalysts. Some of the widely used zeolite catalysts (based on aluminosilicates, phosphates, etc.,), such as HZSM-5 are also recognized to possess high acidity. Nafion- H was made from Nafion-K by proton exchange using dilute nitric acid and has been conveniently used as an effective solid superacid catalyst for various transformations generally carried out using liquid acids including Friedel–Crafts alkylation, acylation, and nitration [66–70]. Olah’s work on superelectrophilic activation [52, 71] showed that not only electrophiles can be further activated in superacidic solutions but also solid acid systems can bring about such activation. Solid strong acids, possessing both Brønsted and Lewis acid sites, are of increasing significance. To explain how solid acids such as Nafion-H or HZSM-5 can show remarkable catalytic activity in hydrocarbon transformations, the nature of activation at the acidic sites of such solid acids must be considered. Nafion-H contains

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Figure 7. (a) Naﬁon-H, a perﬂuorinated resinsulfonic acid, (b) Showing clustering

of SO3H groups.

acidic -SO3H groups in clustered pockets (ionomeric channels, Figure 7). In the acidic zeolite HZSM-5, the active Brønsted and Lewis acid sites are in close proximity (≈2.5 Å). In these (and other) solid superacid catalyst systems, bi- or multidentate interactions are thus possible, forming highly reactive intermediates. This amounts to the solid-state equivalent of protosolvation resulting in superelectrophilic activation leading to interesting synthetic transformations (Scheme 11). Olah showed that a variety of electrophiles, capable of further in- teraction (coordination) with strong Brønsted or Lewis acids, can be greatly activated by them. Examples mentioned were onium and carboxonium ions, acyl cations, halonium, azonium, carbazo- nium ions, and even certain substituted carbocations. This activation produces ‘superelectrophiles’ (name suggested by Olah), that is, electrophiles of doubly electron-deﬁcient (dipositive) nature or even more, whose reactivity signiﬁcantly exceeds that of their parents [52]. In fact, it is now understood that superelectrophiles are the de facto ‘reactive intermediates’ of many elec-

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trophilic reactions in superacidic systems (including those involv- ing solid superacids) and should be diﬀerentiated from energet- ically lower-lying, much more stable, persistent intermediates, which frequently are observable and even isolable but are not nec- essarily reactive enough without further activation.

Methanol Economy

A major step in the Olah’s work in the last two decades was mainly focused on the ‘Methanol Economy’ development of a practical, efficient, and environmentally neutral concept is the novel method – the ‘Methanol Economy’ [72–74] concept. It envis- chemistry-based approach for the ages the replacement of petroleum oil by feasible, practical ap- technological capture plications of the renewable carbon chemistry and the technology and recycling of carbon based on an anthropogenic (man-made) chemical carbon cycle dioxide. [75]. Through continued efforts for over two decades, this concept has now become a proven reality. Further studies paved the path for renewable carbon fuels and derived economy making it suitable and feasible for the long-term benefit of mankind. Na- ture, through photosynthesis, recycles carbon dioxide into plants and other derived systems and eventually to fossil fuels, which are used by mankind for energy generation and its derived products that are essential for modern life. As it is well understood, terrestrial life is inevitably bound to the essential element carbon through its compounds, which eventually ends up as carbon dioxide upon their oxidative, biological or anthropogenic use. A major step in the Methanol Economy concept is the novel chemistry- based approach for the technological capture and recycling of carbon dioxide (CCR, i.e., carbon capture and recycling). This supplements nature’s photosynthetic recycling and provides an inexhaustible source for carbon-based fuels and derived products. Natural replenishing of our diminishing fossil fuel resources through natural carbon cycle would take hundreds of millions of years. The severity of our fuel and feedstock problem cannot be resolved by the use of biofuels or other renewable sources as they cannot meet global requirements. The Methanol Economy offers a feasible solution to our carbon conundrum as it expounds the use of methanol as a versatile fuel and feedstock, which can be

1140 RESONANCE | December 2017 GENERAL ARTICLE prepared from varied carbon sources including recycling of carbon dioxide. In collaboration with Prakash (one of the authors of this article, who started as Olah’s graduate student, became his close friend and colleague for over four decades) this eﬀort continues with increasing practical industrial interest and applications at the Loker Hydrocarbon Research Institute. Methanol and derived DME are excellent transportation and industrial fuels for internal combustion engines (ICE), spark as- sisted diesel engines, and household uses. Methanol is also a fuel in direct oxidation fuel cells that was developed by Olah and Prakash in collaboration with NASA–JPL scientists. Methanol and DME produced from methane (natural gas or shale gas) via ‘metgas’ without going to conventional syngas (a mixture of CO and H2) or by recycling CO2 can subsequently also be used to produce ethylene as well as propylene (Figure 8) [76, 77]. These are the building blocks for the petrochemical industry for the production of synthetic aliphatic and aromatic hydrocarbons and for a wide variety of derived products and materials. At present, the major sources for these materials and products are oil and natural gas. Carbon dioxide, the major global warming culprit, can be chemically transformed from a detrimental greenhouse gas into a valuable, renewable, and inexhaustible carbon source of the future allowing environmentally neutral use of carbon fuels and derived hydrocarbon products. Oxidation of methane is highly exothermic and it goes all the way to CO2 (Figure 9). Controlled oxidation of methane to methanol is not practical. The practical synthesis of methanol by Fischer– Tropsch chemistry was developed in Germany in 1920s [77]. It was based on syngas which by separation and adjusting the required ratio of 2:1 mixture of H2 and CO in the feed gave methanol. It was originally based on coal but subsequently shifted to more convenient natural gas. The conversion of natural gas using steam or dry (CO2) reforming as well as partial oxidation produces H2/CO mixtures with a molar ratio between 3 and 1, but not the exact ratio. However, to produce methanol, a speciﬁc2:1H2:CO mixture (named metgas by Olah) is required. Work in the Loker Institute

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Figure 8. Natural gas

(CH4)andCO2 as sources for methanol and derived products.

Olah, Prakash and has been focused towards the realization of a simple and thermo- co-workers have dynamically feasible way to produce methanol. succeeded in developing a facile new way called In conventional reforming processes, this ratio could not be ‘bi-reforming’ to reached effectively. Olah, Prakash and co-workers have suc- produce metgas from ceeded in developing a facile new way called ‘bi-reforming’ methane in a single step. to produce metgas from methane (natural or shale gas) in a single step by combining the steam and dry-reforming reactions by treating methane or natural gas, CO2 and steam in a 3:1:2 ratio over a Ni/MgO or related catalysts at 800–950 oC in a pressur- ized tubular flow reactor at 5–30 atm [78, 79]. The overall bi-reforming process, being highly endothermic, re- quires substantial external energy as well as multistep feed preparation. As a significant further advance in our method, we found that an exclusive self-sufficient conversion of natural or shale gas (methane) to metgas for methanol synthesis can be achieved by complete oxygenation of part of methane using a process we call oxidative bi-reforming [78, 79]. Apart from the highly ender-

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Figure 9. Thermodynam- ics of direct oxidation of methane.

gonic nature, traditionally practiced partial oxidation and reforming (autothermal reforming) necessitates costly separation steps and adjustments. The complete combustion of one equivalent of methane (natural or shale gas) with aerial oxygen gives the needed feed and process heat for the subsequent bi-reforming step. Thermochemical data show that the exothermic reaction heat of methane combustion is more than sufficient for the subsequent endothermic bi-reforming process. It also provides the required CO2-2H2O mixture, which is captured and admixed with 3 equivalent of methane (natural gas or shale) giving the needed In 2012, in Iceland, specific feed for bi-reforming to produce exclusively metgas for Carbon Recycling the subsequent methanol synthesis step. This self-sufficient ox- International started operation of the first idative bi-reforming of methane to metgas can be carried out in a commercial CO2 to single bundled multi-tubular reactor or in separate reactors. The methanol plant, named formed metgas is then converted to methanol in a well-known and the ‘George Olah industrially practiced synthesis step using Cu/ZnO/Al O or re- Renewable Methanol 2 3 Plant’. lated catalysts (Scheme 12). Thus, methanol is produced from the still abundant natural or shale gas resources that can last well into next century and can be used as a replacement for petroleum oil

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Scheme 12. Oxidative bi-reforming process for methanol synthesis. and its derived products while also decreasing their environmental harm (global warming) via CO2 capture and recycling (CCR) in a feasible, economic way according to the framework of the Methanol Economy concept. In 2012, in Iceland, Carbon Recycling International (CRI) built and started operation of the first commercial CO2 to methanol plant, named the ‘George Olah Renewable Methanol Plant’ (Fig- ure 10). This plant operates on Iceland’s relatively inexpensive and abundant geothermal energy to produce hydrogen by electrolysis of water and the CO2 feed, which accompanies the natural geothermal steam. Development of efficient methods for CO2 capture and recycling to methanol using hydrogen is currently un- derway at the Loker Institute. Hydrogen can be generated from water electrolysis using alternative energies such as solar, wind, hydro, geothermal and even nuclear, none of which emits carbon dioxide. ‘Methanol Economy’ offers a feasible way to liberate humankind from its dependence on diminishing oil and natural gas resources. At the same time, by chemically recycling CO2, one of the major man-made causes of climate change by global warming will be significantly mitigated while rendering carbon-containing fuels and materials regenerative. This whole concept developed by Olah (post-Nobel Prize work) will have a lasting impact on tack-

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Figure 10. The George Olah carbon dioxide to renewable methanol plant in Iceland.

ling the energy and global warming problem. Of course, the vast quantities of energy required to drive the Methanol Economy will have to be harvested from renewable and atomic sources, namely sources that do not emit CO2.

Carbocation Chemistry and Methanol in Space

In recent years, presence of numerous organic hydrocarbon derivatives and their ions (carbocations and carbanions) in interstellar space, surfaces of extraterrestrial planets, and moons have been revealed during studies using onboard analytical instruments in spacecrafts, which pass by these planets and moons. Oka et al., [80, 81] pioneered the astrospectroscopic study of the parent + carbonium ion (CH5 ), fundamental to Olah’s related nonclassical carbonium ion chemistry (vide supra). For example, studies using Cassini spacecraft with its onboard instruments collected signiﬁcant and extensive spectroscopic data from Titan’s upper atmosphere. Careful analysis of the data from the Ion Neutral Mass Spectrometer (INMS) and the Cassini Plasma Spectrometer

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Figure 11. Some astrophysically observed carbocations in the upper atmosphere of Titan similar to the ones observed by Olah and co-workers.

(CAPS) instruments on board of the spacecraft showed the presence of a wide variety of carbocations in the upper atmosphere of Titan similar to those studied by Olah under condensed-state terrestrial conditions in the superacid media (Figure 11). Ali + et al., [30] showed that they include alkyl cations CnH2n+1,the .+ + methane radical cation CH4 , methonium ion CH5 , corner pro- + + tonated cyclopropane C3H7 , cyclopropenium ion C3H3 , benze- + nium ion C6H7 , benzyl cation (which could likely be the tropy- + + lium cation) C7H7 , and even the norbornyl cation C7H11.Inhis study, Ali et al., emphasized the importance and role of Olah’s nonclassical carbonium ion chemistry as the basis of the formation of similar ‘organic ions’ in Titan’s upper atmosphere. Olah’s views on extraterrestrial abiotic hydrocarbon chemistry and his suggestion regarding the vital role of methanol in the extraterrestrial abiotic formation of hydrocarbon derivatives and ions, various complex organic molecules, and eventually the origin of life, are quite intriguing [82–84]. This is underscored by the study and discovery of methanol in space in large amounts and

1146 RESONANCE | December 2017 GENERAL ARTICLE studies regarding its possible formation from simple molecules CO2 and H2 present in enormous amounts around protostars and newly formed stars in the interstellar space [85–87]. It is now known that there are many alternate possible routes for the formation of molecules in the interstellar medium [88] and many forbidden reactions can occur by quantum-mechanical tunneling and the formation of hydrogen-bonded association adducts [89, 90]. In his ﬁnal days, Olah was much excited by his mission to unravel the mysteries in the chemistry and chemical biology of the universe, most importantly, the origin of life.

Conclusion

Olah’s pioneering work spans over six decades in both 20th and 21st centuries. His ingenuity, creativity, and hard work helped to solve many puzzles daunting chemists for many years. His audac- ity to move forward with his innovative ideas, despite the tough challenges he faced, paved the way to real solutions for many problems facing mankind. His mission to ﬁnd a safe solution to the energy-greenhouse gas conundrum with humankind’s dependence on diminishing fossil fuels continues with the suggested and the proven concept of Methanol Economy as well as the ongoing developments in the area of sustainable and renewable energy sources and fuels. Countries like China, Sweden, Israel, Iran, and India are adopting this proven concept. He worked tire- lessly for achieving a permanent ‘carbon neutral’ solution for the energy crisis we are facing today, and the results are amazing. His work revolutionized the area of fuels, the synthetic methodology for materials, and therapeutic drugs. He also trained more than 250 graduate and postdoctoral students, who arrived to work with him from various parts of the world. Olah was singularly honored with a Nobel Prize for his carbocation chemistry in 1994. In 2013, he shared with Prakash, the Eric and Sheila Samson Prime Min- ister’s Prize from the State of Israel for developing the Methanol Economy Concept. George Andrew Olah was not only a great scientist of the time, but a wonderful human being, whose great scientiﬁc contributions to humankind will always be remembered

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and his memory will be greatly cherished.

Suggested Reading

[1] G A Olah and A Pavlath, Synthesis of Organic Fluorine Compounds. III. The Preparation of Fluoro Methanol, Acta Chim. Ac. Sci. Hung., 1953, 3, 203., Chem Abstr., 1954, 48, 7533 (in English). [2] C Sellei, G A Olah, E Eckhart and L Kapas, The Effect of Organic Fluorine Compounds on Experimental Tumors, Arch. F. Geschwulstforch, Vol.5, p.263, 1953. [3] G A Olah, A Pavlath, J A Olah and F Herr, Synthesis and Investigation of Organic Fluorine Compounds. XXIII, The Preparation of Local-Anesthetical, Aromatic Fluorocarbonic Acid Esters, J. Org. Chem., Vol.22, pp.879–881, 1957. [4] G A Olah and A Pavlath, Synthesis of Organic Fluorine Compounds. VIII. Preparation of Chlorofluoromethanes (Compounds of the Freon Type), Acta Chim. Ac. Sci. Hung., 4, 119, 1954; Chem Abstr., Vol.49, p.6094 (in English), 1955. [5] G A Olah, S Kuhn and S Pavlath, Isolation of the Stable Boron Trifluoride Hydrogen Fluoride Complexes of the Methylbenzenes, The Onium Salt (or σ- Complex) Structure of the Friedel-Crafts Complexes, Nature, Vol.178, pp.694– 695, 1956. [6] G W Wheland, A Quantum Mechanical Investigation of the Orientation of Substituents in Aromatic Molecules, J. Am. Chem. Soc., Vol.64, pp.900–908, 1942. [7] G A Olah and S Kuhn, Isolation of the Stable Boron Trifluoride-Ethylfluoride and Boron Trifluoride-Formylfluoride Complexes of the Methylbenzenes: Mechanism of the Friedel-Crafts Reactions, Nature, Vol.178, pp.1344–13455, 1956. [8] It is worth noting that Wheland referred to the species not as an intermediate, but a transition state. Its nature as an intermediate with a well-defined energy minimum was firmly established after Olah isolated them as tetrafluoroborate salts. [9] L Gattermann and W Berchelmann, Synthese aromatischer Oxyaldehyde, Ber. Dtsch. Chem. Ges., Vol.31, pp.1765–1769, 1898. [10] L Gattermann and J A Koch, Eine Synthese aromatischer Aldehyde, Chem. Ber., Vol.30, pp.1622–1624, 1897. [11] E D Hughes, C K Ingold and R T Reed, Kinetics and mechanism of aromatic + nitration. Part II, Nitration by the nitronium ion, NO2 , derived from nitric acid, J. Chem. Soc. pp.2400–2440, 1950. [12] S J Kuhn and G A Olah, Aromatic Substitution. VII. Friedel-Crafts Type Ni- tration of Aromatics, J. Am. Chem. Soc., Vol.83, pp.4564–4571, 1961. [13] G A Olah and S Kuhn, Nitryl Borofluoride as a Nitrating Agent, Chem. Ind., 98, 1956. [14] G A Olah, S J Kuhn and S H Flood, Aromatic Substitution. VIII. Mechanism of Nitronium Tetrafluoroborate Nitration of Alkylbenzenes in Tetramethylene

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Sulfone Solution, J. Am. Chem. Soc., Vol.83, pp.4571–4580, 1961. [15] J H Ridd, Mechanism of Aromatic Nitration, Acc. Chem. Res., Vol.4, pp.248– 253, 1971. [16] C L Perrin, Necessity of Electron Transfer and a Radical Pair in the Nitration of Reactive Aromatics, J. Am. Chem. Soc., 99, 55165518, 1977. [17] G A Olah and T Mathew, A Life of Magic Chemistry: Autobiographical Re- flections Including Post-Nobel Prize Years and the Methanol Economy, 2nd updated ed., John Wiley & Sons: New York, USA, Chapter 2, 2015. [18] G A Olah, My Search for Carbocations and Their Role in Chemistry (Nobel Lecture). Angew. Chem. Int. Ed. Engl., Vol.34, pp.1393–1405. [19] G A Olah, W S Tolgyesi, S J Kuhn, M E Moffat, I J Bastien and E B Baker, Stable Carbonium Ions. IV. Secondary and Tertiary-Alkyl and Ary- lalkyl Oxocarbonium Hexafluoroantimonates. Formation and Identification of Trimethylcarbonium Ion by Decarbonylation of t-Butyl Oxocarbonium Ion, J. Am. Chem. Soc., Vol.85, pp.1328–1334, 1963. [20] G A Olah, E B Baker, J C Evans, W S Tolgyesi, J S McIntyre and I J Bastien, Stable Carbonium Ions, V. Alkylcarbonium Hexafluoroantimonates, J. Am. Chem. Soc., Vol.86, pp.1360–1373, 1964. [21] G A Olah and G K S Prakash, Eds. Carbocation Chemistry, John Willey & Sons: Hoboken, NJ, 2004. [22] G A Olah, Alkylcarbonium- und Oxocarbonium-Salze, Angew. Chem., Vol.75, p.800, 1963. [23] G A Olah and J Lukas, Stable Carbonium Ions. XXX1X, Formation of Alkyl- carbonium Ions via Hydride Ion Abstraction from Alkanes in Fluorosulfonic Acid-Antimony Pentafluoride Solution, Isolation of Some Crystalline Alkylcar- bonium Ion Salts, J. Am. Chem. Soc., Vol.89, pp.2227–228, 1967. [24] N F Hall and J B Conant, A Study of Superacid Solutions, I. The Use of the Chloranil Electrode in Glacial Acetic Acid and the Strength of Certain Weak Bases, J. Am. Chem. Soc., Vol.49, pp.3047–3061, 1927. [25] R J Gillespie, Fluorosulfuric acid and related superacid media, Acc. Chem. Res., Vol.1, pp.202–209, 1968. [26] G A Olah, G K S Prakash, A Molnr and J Sommer, Eds., Superacid Chemistry, 2nd Ed., John Wiley & Sons Inc., Hoboken, New Jersey, Chapters 1 & 2, 2009. [27] G A Olah and Y Halpern, Stable Carbocations. CXX. Preparation of Alkyl (Aryl) Carbenium Ions from Olefins, J. Org. Chern., Vol.36, pp.2354–2356, 1971. [28] G A Olah, G K S Prakash, R E Williams, L D Field and K Wade, Eds., Hyper- carbon Chemistry, Wiley, New York, 1987. + [29] T R Geballe and T Oka, Detection of H3 in Interstellar Space, Nature, Vol.384, pp.334–335, 1996. [30] A Ali, E C Sittler, Jr., D Chornay, B R Rowe, C Puzzarini, Organic chemistry in Titan’s upper atmosphere and its astrobiological consequences: I. Views towards Cassini plasma spectrometer (CAPS) and ion neutral mass spectrometer (INMS) experiments in space, Planet Space Sci., Vol.109–110, pp.46–63, 2015. [31] G A Olah, Conference Lecture at 9th Reaction Mechanism Conference, Brookhaven, New York, August 1962.

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[32] SWinsteinandDSTrifan,TheStructureofBicyclo[2,2,1]2-heptyl(Norbornyl) Carbonium Ion, J. Am. Chem. Soc., Vol.71, pp.2953–2953, 1949. [33] S Winstein, E Clippinger, R Howe and E Vogelfanger, The Nonclassical Nor- bornyl Cation, J. Am. Chem. Soc., Vol.87, pp.376–377, 1965. [34] M Saunders, P V R Schleyer and G A Olah, Stable Carbonium Ions. XI, The Rate of Hydride Shifts in the 2-Norbornyl Cation, J. Am. Chem. Soc., Vol.86, pp.5680–5681, 1964. [35] G A Olah, A M White, J R DeMember, A Commeyras, C Y Lui, Stable Car- bonium ions. C. Structure of the Norbornyl Cation, J. Am. Chem. Soc., Vol.92, pp.4627–4640, 1970. [36] G A Olah, G K S Prakash, M Arvanaghi and F A L Anet, High-Field 1Hand 13C NMR Spectroscopic Study of the 2-Norbornyl Cation, J. Am. Chem. Soc., Vol.104, pp.7105–7108, 1982. [37] K Raghavachari, R C Haddon, P v R Schleyer and H F Schaeffer, III. Effects of Electron Correlation on the Energies of 2-Norbornyl Cation Structures, Eval- uation of the Nonclassical Stabilization Energy, J. Am. Chem. Soc., Vol.105, pp.5915–5917, 1983. [38] G A Olah, G Liang, G D Mateescu and J L Riemenschneider, Stable Carbo- cations. CL. Fourier Transform 13C Nuclear Magnetic Resonance and X-ray Photoelectron Spectroscopic Study of the 2-Norbornyl Cation, J. Am. Chem. Soc., Vol.95, pp.8698–8702, 1973. [39] C S Yannoni, V Macho and P C Myhre, Resolved 13C NMR Spectra of Car- bonium Ions at Cryogenic Temperatures. The Norborynl Cation at 5 K, J. Am. Chem. Soc., Vol.104, pp.7380–7381, 1982. [40] F Scholz, D Himmel, F W Heinemann, P v R Schleyer, K Meyer and I Kross- ing, Crystal Structure Determination of the Nonclassical 2-Norbornyl Cation, Science, Vol.341, pp.62–64, 2013. [41] K Lammertsma, M Barzaghi, G A Olah, J A Pople, P v R Schleyer and M Si- 2+ monetta, Structure and Stability of Diprotonated Methane CH6 , J. Am. Chem. Soc., Vol.105, pp.5258–5263, 1983. 3+ [42] G A Olah and G Rasul, Triprotonated Methane, CH7 : The Parent Heptaco- ordinate Carbonium Ion, J. Am. Chem. Soc., Vol.118, pp.8503–8504, 1996. [43] F Scherbaum, A Grohmann, G Muller¨ and H Schmidbaur, Synthesis, Struc- + ture, and Bonding of the Cation [{(C6H5)3PAu}5C] , Angew. Chem., Int. Ed. Engl., Vol.28, pp.463–464, 1989. [44] F Scherbaum, A Grohmann, B Huber, C Kruger¨ and H Schmid- baur, “Aurophilicity” as a Consequence of Relativistic Effects: The 2+ Hexakis(triphenylphosphaneaurio)methane Dication [(Ph3PAu)6C] , Angew, Chem., Int. Ed. Engl., Vol.27, pp.1544-1546, 1988. 2+ [45] H Hogeveen and P W Kwant, (CCH3)6 , an Unusual Dication, J. Am. Chem. Soc., Vol.96, pp.2208–2213, 1974. [46] M Malischewski and K Seppelt, Crystal Structure Determination of 2+ the Pentagonal-Pyramidal Hexamethylbenzene Dication C6(CH3)6 , Angew. Chem. Int. Ed. Engl., Vol.56, pp.368–370, 2017. [47] G A Olah, The General Concept and Structure of Carbocations Based on Differentiation of Trivalent (‘Classical’) Carbenium Ions from Three-Center

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Bound Penta- or Tetracoordinated (‘Nonclassical’) Carbonium Ions. The Role of Carbocations in Electrophilic Reactions, J. Am. Chem. Soc., Vol.94, pp.808– 819, 1972. [48] G A Olah, Crossing Conventional Boundaries in Half a Century of Research, J. Org. Chem., Vol.70, pp.2413–2429, 2005. [49] C D Nenitzescu and A Dr¢gan, Uber¨ die Einwirkung von Aluminiumchlorid auf n-Hexan und n-Heptan, allein und in Gegenwart von Halogenderivaten. Eine berfhrung von Paraffin- in Cycloparaffin-Kohlnewasserstoffe, Ber. Dtsch, Chem. Ges., Vol.66, pp.1892–1900, 1933. [50] F Asinger, Paraffins, Pergamon Press, New York, p.695, 1968. [51] G A Olah and G K S Prakash, in The Chemistry of Alkaners and Cycloalkanes, S Patai and Z Rappoport, eds. Wiley, Chchester, Chapter 13, p.490, 1992. [52] G A Olah and D A Klumpp, Superelectrophiles and their Chemistry, Wiley- Interscience, Hoboken, New Jersey, 2008. [53] G A Olah, Y Halpern, J Shen and Y K Mo, Electrophilic Reactions at Sin- gle Bonds. XII. Hydrogen-Deuterium Exchange, Protolysis (Deuterolysis), and Oligocondensation of Alkanes with Superacids, J. Am. Chem. Soc., Vol.95, pp.4960–4970 and references cited therein, 1973. [54] G A Olah, Electrophilic methane conversion, Acc. Chem. Res., Vol.20, pp.422– 428, 1987. [55] G A Olah, B Gupta, M Farima, J D Felberg, M I Wai, A Husain, R Karpeles, K Lammerstsma, A K Melhotra and N Trivedi, J., Electrophilic reactions at single bonds. 20. Selective monohalogenation of methane over supported acidic or platinum metal catalysts and hydrolysis of methyl halides over .gamma.- alumina-supported metal oxide/hydroxide catalysts. A feasible path for the oxidative conversion of methane into methyl alcohol/dimethyl ether, J. Am. Chem. Soc., Vol.107, pp.7097–7105, 1985. [56] G A Olah, R Malhotra, S C Narang, Nitration: Methods and Mechanisms, Wiley-VCH, 1989, New York. [57] N C Deno, B A Greigger and S G Stroud, New method for elucidating the structures of coal, Fuel, Vol.57, pp.455–459, 1978. [58] G A Olah and R Ohnishi, Oxyfunctionalization of Hydrocarbons. 8. Elec- trophilic Hydroxylation of Benzene, Alkylbenzenes and Halobenzenes with Hy- drogen Peroxide in Superacids, J. Org. Chem., Vol.43, pp.865–867, 1978. [59] L F Albright, ed., Industrial and Laboratory Alkylations, ACS Symposium Se- ries, Vol.55, Am. Chem. Soc., Washington, DC. 1977. [60] J Schulze, M Homan, C4-Hydrocarbons and Derivatives, SpringerVerlag: Berlin, 1989, Chapters 3, 4. [61] H L Hoffman, Catalyst Market Estimated, Hydrocarbon Proc., Vol.69, pp.53– 54, 1990. [62] A Corma, Inorganic Solid Acids and Their Use in Acid-Catalyzed Hydrocar- bon Reactions, Chem. Rev., Vol.95, pp.559–614, 1995. [63] G A Olah, J T Welch, Y D Vankar, M Nojima, Kerekes, I. and J A Olah, Syn- thetic Methods and Reactions, 63. Pyridinium Poly (hydrogen fluoride) (30% Pyridine-70% Hydrogen Fluoride): A Convenient Reagent for Organic Fluo- rination Reactions, J. Org. Chem., Vol.44, pp.3872–3981, 1979.

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[64] G A Olah, T Mathew, A Goeppert, B Torok, I Bucsi, Li X-Y, Q Wang, E R Marinez, P Batamack, R Aniszfeld and G K S Prakash, Ionic Liquid and Solid HF Equivalent Amine-Poly(Hydrogen Fluoride) Complexes Effecting Efficient Environmentally Friendly Isobutane-Isobutylene Alkylation, J. Am. Chem. Soc., Vol.127, pp.5964–5969, 2005. [65] G A Olah, Environmentally safe catalytic alkyation using liquid onium poly (hydrogen fluorides), U.S. Patent 5073674 1991. [66] G A Olah, P S Iyer, G K S Prakash, Perfluorinated Resinsulfonic Acid (Nafion- H Catalysis in Synthesis, Synthesis, pp.513–531, 1986. [67] G A Olah, D Mediar, R Malhotra, J A Olah and S C Narang, Heterogeneous Catalysis by Solid Superacids, 14. Perfluorinated Resinsulfonic Acid Catalyzed Friedel-Crafts Alkylation of Toluene and Phenol with Alkyl chloroformates and Oxalates, J. Catal., Vol.61, pp.96–102, 1980. [68] G A Olah, R Malhotra, S C Narang and J A Olah, Heterogeneous Catalysis by Solid Superacids. 14. Perfluorinated Resinsulfonic Acid Catalyzed Friedel- Crafts Acylation of Benzene and Substituted Benzenes, Synthesis, pp.672–673, 1978. [69] G A Olah, B Torok, T Shamma, M Torok and G K S Prakash, Solid acid (superacid) catalyzed regioselective adamantylation of substituted benzenes, Catal. Lett., Vol.42, pp.5–13, 1996. [70] G A Olah, T Mathew, M Farnia and G K S Prakash, Catalysis by solid superacids. Part 33. Nafion-H catalyzed intramolecular Friedel-Crafts acylation. Formation of cyclic ketones and related heterocycles, Synlett, Vol.7, pp.1067– 1068, 1999. [71] G A Olah, Superelectrophiles, Angew. Chem. Int. Ed. Engl., Vol.32, pp.767–788, 1993. [72] G A Olah, A Goeppert and G K S Prakash, Beyond Oil and Gas: The Methanol Economy, 2nd updated and enlarged ed., Wiley-VCH: Weinheim, Germany, 2009. [73] G A Olah, G K S Prakash and T Mathew, Anthropogenic Carbon Cycle and the Methanol Economy (Part XXX). In Across Conventional Lines- The Sixth Decade and the Methanol Economy, Volume 3, World Scientific: Singapore, 2014. [74] G A Olah and T Mathew, A Life of Magic Chemistry: Autobiographical Reflec- tions Including Post-Nobel Prize Years and the Methanol Economy, 2nd updated ed., John Wiley & Sons: New York, Chapters 13-15, 2015. [75] G A Olah, G K S Prakash and A Goeppert, Anthropogenic Chemical Carbon Cycle for a Sustainable Future, J. Am. Chem. Soc., Vol.133, pp.12881–12898, 2011. [76] C D Chang and A J Silvestri, The Conversion of Methanol and Other O- Compounds to Hydrocarbons over Zeolite Catalysts, J. catal., Vol.47, pp.249– 259 and the references cited therein, 1977. [77] G A Olah, Bifunctional acid-base catalyzed conversion of hetero-substituted methanes into olefins U.S. Patent 4,373,109 A (1983). [78] G A Olah, G K S Prakash, A Goeppert, M Czaun and T Mathew, Self-Sufficient and Exclusive Oxygenation of Methane and Its Source Materials with Oxy-

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gen to Methanol via Metgas Using Oxidative Bireforming, J. Am. Chem. Soc., Vol.135, pp.10030–10031, 2013. [79] G A Olah, A Goeppert, M Czaun, T Mathew, R B May and G K S Prakash, Sin- gle Step Bi-reforming and Oxidative Bi-reforming of Methane (Natural Gas)

with Steam and Carbon Dioxide to Metgas (CO-2H2) for Methanol Synthesis: Self-Sufficient Effective and Exclusive Oxygenation of Methane to Methanol with Oxygen, J. Am. Chem. Soc., Vol.137, pp.8720–8729, 2015. + [80] E T White, J Tang and T Oka, CH5 : the infrared spectrum observed, Science, Vol.284, pp.135–137, 1999. + [81] T Oka, Taming CH5 , the ‘enfant terrible’ of chemical structures, Science, Vol.347, pp.1313–1314, 2015. [82] G A Olah, T Mathew and G K S Prakash, Chemical Aspects of Astrophysically Observed Extraterrestrial Methanol, Hydrocarbon Derivatives, and Ions, J. Am. Chem. Soc. Vol.138, pp.1717–1722, 2016. [83] G A Olah, T Mathew and G K S Prakash, Relevance and Significance of Ex- traterrestrial Abiological Hydrocarbon Chemistry, J. Am. Chem. Soc., Vol.138, pp.6905–6911, 2016. [84] G A Olah, T Mathew and G K S Prakash, Chemical Formation of Methanol Address for Correspondence and Hydrocarbon (‘Organic’) Derivatives From CO2 and H2 – Carbon Sources *Ripudaman Malhotra for Subsequent Biological Cell Evolution and Life’s Origin, J. Am. Chem. Soc., Thomas Mathew Vol.139, pp.566–570, 2017. G K Surya Prakash [85] S B Charnley, M E Kress, A G G M Tielens, T J Millar, Interstellar Alcohols, ∗ San Carlos, CA94070, USA Astrophys. J., Vol.448, pp.232–239, 1995. Loker Hydrocarbon Research [86] A Heward, Upgraded MERLIN Spies Cloud of Alcohol Spanning 288 Billion Institute and Department of Miles, PN 06/14 (NAM7); Royal Astronomical Society: London, April 4, 2006. Chemistry, University of [87] L Harvey-Smith and R J Cohen, Discovery of Large-scale Methanol and Southern California, Los Hydroxyl Maser Filaments in W3(OH), Mon. Not. R. Astron. Soc., Vol.371, Angeles, CA 90089, USA pp.1550–1338, 2006. Email: [88] B E Turner and L M Ziurys, Interstellar Molecules and Astrochemistry, In *ripudaman.malhotra@gmail. Galactic and Extragalactic Radio Astronomy, K Kellerman, G Verschurr, eds. com Springer-Verlag, New York, pp.200–254, 1988. [email protected] [89] I R Sims, Tunnelling in space, Nature Chem., Vol.5, pp.734–736, 2013. [email protected] [90] R J Shannon, M A Blitz, A Goddard and D E Heard, Accelerated Chemistry in the Reaction between the Hydroxyl Radical and Methanol at Interstellar Tem- peratures Facilitated by Tunnelling, Nature Chem., Vol.5, pp.745–749, 2013.

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