ORIGINAL PAPER Facile and Direct Synthesis of Symmetrical Acid

Chemical Papers 69 (3) 479–485 (2015) DOI: 10.1515/chempap-2015-0042

ORIGINAL PAPER

Facile and direct synthesis of symmetrical acid anhydrides using a newly prepared powerful and eﬃcient mixed reagent

Hamed Rouhi-Saadabad, Batool Akhlaghinia*

Department of Chemistry, Faculty of Sciences, Ferdowsi University of Mashhad, 9177948974 Mashhad, Iran

Received 31 March 2014; Revised 16 July 2014; Accepted 7 August 2014

An eﬃcient mixed reagent for direct synthesis of symmetrical carboxylic anhydrides from carboxylic acids has been prepared. Carboxylic acids are converted to anhydrides using triphenylphosphine/trichloroisocyanuric acid under mild reaction conditions at room temperature. Short reaction time, excellent yields of products, low cost, availability of reagents, simple experimental procedure, and easy work-up of the products are the main advantages of the presented method. c 2014 Institute of Chemistry, Slovak Academy of Sciences

Keywords: trichloroisocyanuric acid, triphenylphosphine, carboxylic acid, carboxylic anhydride, functional group transformation

Introduction 1968; Jorba et al., 1990; Katritzky et al., 1992; Ke- shavamurthy et al., 1982; Kim et al., 2003; Kita et Among the most important classes of reagents, car- al., 1984, 1986; Mestres & Palomo, 1981; Newman & boxylic anhydrides are useful compounds either as Louge, 1971; Rinderknecht & Ma, 1964; Rinderknecht acylating agents or as intermediates in organic syn- & Guttenstein, 1967; Kocz et al., 1994; Sandler & thesis due to the high electrophilic character of their Karo, 1972), new and more convenient methods for carbonyl groups (Ogliaruso & Wolfe, 1991; Mariella & the synthesis of this class of compounds still pro- Brown, 1971; Shambhu & Digenis, 1974; Tamura et ceeds. Carboxylic anhydrides are usually prepared al., 1987a, 1987b; Holzapfel & Pettit, 1985; Fukuoka through a reaction of carboxylic acids with acylat- et al., 1987; Bryson & Roth,Author 1986). They are preferred ing or dehydratingcopy coupling agents, such as acid chlo- reactive acid derivatives for the preparation of amides, rides (Rambacher & Mäke, 1968), anhydrides (Sandler esters, and peptides (Ogliaruso & Wolfe, 1991; Tar- & Karo, 1972), mixed carboxylic–sulfonic anhydrides bel, 1969; Meienhofer & Gross, 1979). Mixed anhy- (Karimi Zarchi et al., 2010; Kazemi et al., 2004), drides are not suitable for many transacylation ap- triphenylphosphine (PPh3)/trichloroacetonitrile (Kim plications because the attack at the other acyl group & Jang, 2001), thionyl chloride (Fife & Zhang, 1986; leads to the formation of by-products; therefore, the Adduci & Ramirez, 1970; Kazemi & Kiasat, 2003; availability of symmetrical anhydrides is very impor- Kazemi et al., 2007), phosgene (Rinderknecht & Ma, tant in such reactions (Fife & Zhang, 1986). Although 1964; Rinderknecht & Guttenstein, 1967; Kocz et al., many reagents for the synthesis of carboxylic acid an- 1994), phosphorus pentoxide (Burton & Kaye, 1989; hydrides have been developed (Tamura et al., 1987b; Mestres & Palomo, 1981), isocyanate (Keshavamurthy Bryson & Roth, 1986; Fife & Zhang, 1986; Adduci et al., 1982), 1,3-dicyclohexylcarbodiimide (Chen & & Ramirez, 1970; Kazemi & Kiasat, 2003; Kazemi Benoiton, 1979; Hata et al., 1968), ketene (Kita et et al., 2007; Blankemeyer-Menge et al., 1990; Bur- al., 1986), ethoxyacetylene (Tamura et al., 1987b; ton & Kaye, 1989; Chen & Benoiton, 1979; Edman Bryson & Roth, 1986; Edman & Simmons, 1968; & Simmons, 1968; Eglinton et al., 1954; Hata et al., Eglinton et al., 1954; Kita et al., 1984, 1986; Mestres

*Corresponding author, e-mail: [email protected] 480 H. Rouhi-Saadabad, B. Akhlaghinia/Chemical Papers 69 (3) 479–485 (2015)

& Palomo, 1981; Newman & Louge, 1971), sulfated Experimental zirconia (Hu et al., 2011), triazine reagents (Kamiński et al., 2004), 4,5-dichloro-2-[(4-nitrophenyl)sulphonyl] General pyridazin-3(2H )-one (Kim et al., 2003) as well as the reaction of carboxylate salts with powerful acy- The products were purified by column chromatog- lating agents, such as acid chlorides (Rambacher & raphy. Purity of the products was determined by TLC Mäke, 1968; Hajipour & Mazloumi, 2002), or acid an- on silica gel polygram STL G/UV 254 plates (60 hydrides (Sandler & Karo, 1972). Anhydrides have mesh; Merck, Germany). Melting points of the prod- been also prepared by the dehydration of carboxylic ucts were determined using an Electrothermal Type acids (Wallace & Copenhaver, 1941; Rammler & 9100 melting point apparatus (UK). FT-IR spectra Khorana, 1963; Liesen & Sukenik, 1987) or from were recorded on an Avatar 370 FT-IR Thermo Nico- acid chlorides (Serieys et al., 2008; Kim & Jang, let spectrometer (USA). NMR spectra for 13CNMR 2009). and 1H NMR were provided by Brucker Avance (Ger- However, many of these methods have major or many) 100 MHz and 400 MHz instruments in CDCl3 minor disadvantages, and the development of a new and using TMS as an internal standard. Chemical and efficient method for the synthesis of symmetrical shift is given in δ relative to TMS. Mass spectra were anhydrides is of current interest. recorded with a CH7A Varianmat Bremem instrument Trichloroisocyanuric acid (TCCA) in combination (Germany) at 70 eV; in m/z (rel. %). Silica gel in the

with PPh3 has found widespread use in synthetic or- size of 40–73 m that used for column chromatography ganic chemistry (Sugimoto et al., 2012; Sugimoto & was purchased from Merck. All products are known Tanji, 2005; Hiegel et al., 1999). In continuation of compounds and they were characterized by IR spec- our search new methods of functional group trans- tral data and a comparison of their melting points formations (Iranpoor et al., 2004a, 2004b, 2004c, with those of authentic samples. Also, structures of 2005; Akhlaghinia, 2004, 2005a, 2005b; Akhlagh- some selected products were further conﬁrmed by 1H inia & Pourali, 2004; Akhlaghinia & Samiei, 2009; NMR and 13C NMR spectroscopy and by mass spec- Akhlaghinia & Rouhi-Sadabad 2013; Rouhi-Sadabad trometry. & Akhlaghinia, 2014; Kiani et al., 2014), a direct, mild and eﬃcient procedure for the synthesis of var- General procedure for potassium carboxylate ious symmetrical acid anhydrides from carboxylic (II) preparation acids using the prepared mixed reagent is reported here. Potassium hydroxide (112.2 mg, 2 mmol) was

Table 1. Spectral data of selected prepared compounds Compound Spectral data −1 IIIa IR,ν ˜/cm : 3011 (CH-arom), 2843 (CH-aliph), 1789 and 1711 (C—O), 1607 (C—C) 1 H NMR (400 MHz, CDCl3), δ:8.13(d,4H,J = 8.0 Hz, H-arom), 7.01 (d, 4H, J = 8.0 Hz, H-arom), 3.93 (s, 6H, 2 × OCH3) 13 C NMR (100 MHz, CDCl3), δ: 164.6, 162.3, 132.9, 121.3, 114.2, 55.6 −1 IIIb IR,ν ˜/cm : 3023 (CH-arom), 2859 (CH-aliph), 1782 and 1713 (C—O), 1608 (C—C) 1 H NMR (100Author MHz, CDCl3), δ:7.75(s,4H,H-arom),7.26(s,2H,H-arom),2.40(s,12H,4 copy × CH3) + + MS, m/z (Ir/%): 282 (5) (M ) 149 (10) (M –(Me)2PhCO), 133 (100) ((Me)2PhCO), 105 (88) ((Me)2PhCO), 91 (30) (PhCH2) −1 IIIc IR,ν ˜/cm : 3059 (CH-arom), 2912 (CH-aliph), 1774 and 1713 (C—O), 1609 (C—C) 1 H NMR (400 MHz, CDCl3), δ:8.07(d,4H,J = 8.0 Hz, H-arom), 7.34 (d, 4H, J = 8.0 Hz, H-arom), 2.48 (s, 6H, 2 × CH3) 13 C NMR (100 MHz, CDCl3), δ: 162.6, 145.6, 130.7, 129.6, 126.2, 21.9 −1 IIId IR,ν ˜/cm : 3064 (CH-arom), 1785 and 1724 (C—O), 1598 (C—C) 1 H NMR (400 MHz, CDCl3), δ:8.19(dt,4H,J =8.4Hz,J = 1.6 Hz, H-arom), 7.71 (tt, 2H, J =5.6Hz,J =1.6Hz, H-arom), 7.56 (td, 4H, J =7.2Hz,J =1.6Hz,H-arom) −1 IIIk IR,ν ˜/cm : 3023 (CH-arom), 2933 (CH-aliph), 1801 and 1736 (C—O), 1699 (C—C) 1 H NMR (400 MHz, CDCl3), δ: 7.38–7.20 (m, 20H, H-arom), 5.07 (s, 2H, 2 × (Ph)2CH—C—O) 13 C NMR (100 MHz, CDCl3), δ: 167.6, 136.9, 128.8, 128.7, 127.7, 57.9 −1 IIIo IR,ν ˜/cm : 3066 and 3023 (CH-arom), 1768 and 1701 (C—O), 1631 (C—Cvinyl), 1450 (C—Carom) 1 H NMR (100 MHz, CDCl3), δ:7.75(d,2H,J = 16.0 Hz, PhCH—), 7.68–7.31 (m, 10H, H-arom), 6.52 (d, 2H, J = 16.0 Hz, PhCH—) + + MS, m/z (Ir/%): 278 (40) (M ) 149 (23) (M –PhCH—CHCO), 130 (100) (PhCH—CHCO), 103 (95) (PhCH—CH), 91 (75) (PhCH2), 77 (95) (Ph) H. Rouhi-Saadabad, B. Akhlaghinia/Chemical Papers 69 (3) 479–485 (2015) 481

Table 2. Conversion of benzoic acid to benzoic anhydride using the PPh3/TCCA/PhCOOK system under diﬀerent reaction conditions

a Entry Solvent PPh3/TCCA/PhCOOH/PhCOOK mole ratio Time/h Yield /%

1CH3CN 1:1:1:1 5 75 2CH3CN 1:1:1:1.5 3 80 3CH3CN 1:1:1:2 2 85 4CH3CN 1:1:1:2.5 2 85 5CH3CN 1:0.3:1:2.5 2 85 6CH3CN 1:0.3:1:2 2 80 7CH3CN 1:0.3:1:1 5 75 8CH3CN 1:0.3:0.5:1 4 70 b 9CH3CN 1:0.3:0.5:2 50 90 b 10 CH2Cl2 1:0.3:0.5:2 50 95 11 THF 1:0.3:0.5:2 1 90 12 EtOAc 1:0.3:0.5:2 70b 85 a) Yields refer to the isolated products; b) in min. added to a solution of carboxylic acid (2 mmol) in distilled water. The solution was stirred at room temperature for 30 min. Evaporation of the solvent gave crystals of potassium carboxylate salt.

General procedure for benzoic anhydride (IIId) preparation Fig. 1. Direct synthesis of symmetric anhydrides (III )from ◦ → To a cold solution of TCCA (77.4 mg, 0.3 mmol) carboxylic acids (I ); i) PPh3, TCCA, CH2Cl2,0C r.t.; for substituent specification see Table 3. in CH2Cl2 (3–5 mL), PPh3 (262.3 mg, 1 mmol) was added at 0–5 ◦C under stirring. A white suspension was formed to which benzoic acid (121.3 mg, 1 mmol) was added and the stirring continued for 15 min at room 8). Applying the 1 : 0.3 : 0.5 : 2 mole ratio of temperature. Potassium benzoate (322.2 mg, 2 mmol) PPh3/TCCA/RCO2H/RCOOK in CH3CN gave the was added and the stirring was continued for further same result as in CH2Cl2 (Table 2, Entry 9). The 50 min at room temperature. After the completion of selected solvent for this transformation was CH2Cl2 the reaction (monitored by TLC), the mixture was which is less expensive than CH3CN. These re- washed with cold distilled water (2 × 10 mL). The actions revealed that even simple stirring of this organic layer was dried with anhydrous Na2SO4,and PPh3/TCCA/PhCOOH/PhCOOK system in CH2Cl2 passed through a short silica-gel column using hex- at room temperature affects the formation of ben- ane/ethyl acetate (ϕr = 10 : 1) as the eluent. IIId was zoic anhydride in a 95 % isolated yield within 50 min obtained in a 95 % yield (214.7 mg) after the solvent (Table 2, Entry 10). However, the same reaction in was removed under reduced pressure. Selected spec- tetrahydrofuran (THF) and ethyl acetate (EtOAc) af- tral data of six representative Author products are given in forded copy benzoic anhydride in a 85–90 % yield in longer Table 1. reaction time (Table 2, Entries 11 and 12). The present method can be generally applied Results and discussion for a range of structurally diverse carboxylic acids. Aliphatic and aromatic carboxylic acids can be thus Direct preparation of carboxylic anhydrides from converted into their corresponding anhydrides in high carboxylic acids is still in great demand. In this pa- isolated yields. The scope and generality of this pro- per, an efficient and convenient method for the prepa- cess is illustrated using several examples and the re- ration of symmetrical carboxylic anhydrides from the sults are summarized in Table 3. corresponding carboxylic acids using a PPh3/TCCA Structure of the products was determined from mixed reagent in the presence of RCOOK is presented. their spectral data (IR, 1HNMR,and13CNMR), General reaction is outlined in Fig. 1. and by its direct comparison with authentic samples. Several controlled reactions were carried out to es- The 13C NMR signal at around δ 160 was assigned tablish the optimal reaction conditions. The influence to the carbonyl carbon of anhydride. Two strong and −1 of different molar ratios of PPh3/TCCA/PhCOOH/ sharp absorption bands at 1808–1763 cm and at −1 PhCOOK in CH3CNwasstudied:the1:0.3:0.5:2 1737–1701 cm in the FT-IR spectra were assigned mole ratio provided the shortest reaction time and to the asymmetric and symmetric C—O stretching vi- the highest yields obtained (Table 2, Entries 1– brations, respectively. 482 H. Rouhi-Saadabad, B. Akhlaghinia/Chemical Papers 69 (3) 479–485 (2015)

Table 3. Synthesis of carboxylic acid anhydrides from carboxylic acids using the PPh3/TCCA/RCOOK system

Isolated Reported Entry Compound Carboxylic acid Time/min yield/% M.p./ ◦C M.p./ ◦C References

1 IIIa 4-MeOC6H4COOH 40 97 89–91 88–93 Park et al. (2005) 2 IIIb 3,5-Me2C6H3COOH 35 98 131–133 132–133 Tachibana et al. (2006) 3 IIIc 4-MeC6H4COOH 40 90 78–79 78–80 Hu et al. (1997) 4 IIId PhCOOH 50 95 41–43 42–44 Park et al. (2005) 5 IIIe 4-BrC6H4COOH 65 93 219–220 218–220 Hu et al. (1997) 6 IIIf 4-ClC6H4COOH 90 94 191–193 192–193 Park et al. (2005) 7 IIIg 3,4-Cl2C6H3COOH 100 95 146–148 147–149 Rosowsky et al. (1998) 8 IIIh 4-NO2C6H4COOH 120 96 173–176 172–176 Hu et al. (1997) 9 IIIi 3-NO2C6H4COOH 120 92 160–162 161–163 Hu et al. (1997) 10 IIIj PhCH2COOH 80 96 71–72 72–72.5 Jenkins and Cohen (1975) 11 IIIk (Ph)2CHCOOH 85 97 96–98 97–98 Brady and O’Neal (1967) 12 IIIl 4-MeOPhCH2COOH 75 97 77–78 76–78 Roof et al. (1976) 13 IIIm CH3(CH2)15CH2COOH 75 95 69–71 70–72 Hu et al. (1997) 14 IIIn CH3(CH2)7CH— 90 95 20–22 22 Sonntag et al. (1954) CH(CH2)6CH2COOH 15 IIIo (E)-PhCH—CHCOOH 90 95 134–136 135–137 Hu et al. (1997) 16 IIIp 4-ClPhCH—CHCOOH 120 98 185–187 187 Exner and Jehlicka (1970) 17 IIIq 3-NO2PhCH—CHCOOH 180 97 204–206 206 Hurd and Thomas (1933) 18 IIIra phtalic acid 60 95 130–132 131–132 Kimura et al. (2012) 19 IIIs pyridine-4-carboxylic acid 120 92 101–103 102–104 Funasaka and Mukaiyama (2008) 20 IIIt thiophene-3-carboxylic acid 120 97 48–50 50–52 Funasaka and Mukaiyama (2008) a) Reaction was carried out in the presence of triethylamine.

Author copy

Fig. 2. Proposed mechanism for direct synthesis of anhydrides (III ) from carboxylic acids.

In order to gain deeper insight into the general ap- applied in the reaction of different classes of carboxylic plicability of this method, optimized conditions were acids with this mixed reagent system. The results re- H. Rouhi-Saadabad, B. Akhlaghinia/Chemical Papers 69 (3) 479–485 (2015) 483 vealed that the reaction can be employed for a wide the synthesis of symmetrical acid anhydrides using range of carboxylic acids. Aromatic carboxylic acids the PPh3/TCCA/RCO2H/RCOOK system with ex- with electron donating substituents were successfully cellent yields and high product purity has been de- converted into their corresponding carboxylic anhy- scribed. This procedure has the following advantages: drides in a short time and with high yields (Table 3, (i) direct conversion of acids to anhydrides in a short Entries 1–4), whereas the reaction of aromatic car- reaction time at room temperature; (ii) mild reaction boxylic acids with electron withdrawing groups, cin- conditions; (iii) safety of the process, low cost, and namic acids, and hetero aromatic acids required longer availability of reagents; (iv) simple experimental pro- reaction time to reach such excellent yields due to very cedure and; (v) easy work-up of the products. poor nucleophilicity of the corresponding carboxylate Acknowledgements. The authors gratefully acknowledge the ions (Table 3, Entries 5–9 and 15–17 and 19–20). On partial support of this study by the Ferdowsi University of basis of the mechanism proposed in our previous re- Mashhad Research Council (Grant no. p/3/19312). search (Akhlaghinia & Rouhi-Saadabad, 2013) (Fig. 2) and results obtained from Table 3, nucleophilic attack Supplementary data of the carboxylate ion on V yielding triphenylphosphine oxide and the corresponding carboxylic anhy- Supplementary data associated with this article drides is the rate determining step. The stronger the can be found in the online version of this paper (DOI: nucleophiles are, the faster is the product formation. 10.1515/chempap-2015-0042). The FT-IR spectrum of [1,3,5]triazine-2,4,6-triol (VI ) which is in equilibrium with [1,3,5]triazinane-2,4,6- References trione (VII ) showed two very strong and sharp bands −1 at 3200 cm ascribed to the OH and NH and at Adduci, J. M., & Ramirez, R. S. (1970). Anhydride formation −1 1749 cm ascribed to the C—O stretching vibrations, with thionyl chloride. Organic Preparations and Procedures respectively. International, 2, 321–325. DOI: 10.1080/00304947009458638. Also, the reaction with aliphatic acids provides Akhlaghinia, B. (2004). Efficient conversion of tetrahydropyranyl (THP) ethers to their corresponding cyanides with high yields of their corresponding carboxylic acid an- triphenylphosphine/2,3-dichloro-5,6-dicyanobenzoquinone/ hydrides in a short reaction time (Table 3, Entries n-Bu4NCN. Phosphorus, Sulfur, and Silicon and the Related 10–14). Elements, 179, 1783–1786. DOI: 10.1080/10426500490466463. Dicarboxylic acids, such as phthalic acid, in the Akhlaghinia, B., & Pourali, A. R. (2004). Novel and highly se- presence of PPh3/TCCA, triethylamine, and in the lective conversion of alcohols and thiols to alkyl nitrites with absence of potassium carboxylate are cleanly, eas- triphenylphosphine/2,3-dichloro-5,6-dicyanobenzoquinone/ Bu4NNO2 system. Synthesis, 2004, 1747–1749. DOI: 10.1055 ily, and efficiently converted into their corresponding /s-2004-829122. cyclic anhydrides in high isolated yields (Table 3, En- Akhlaghinia, B. (2005a). Triphenylphosphine/2,3-dichloro-5,6- try 18). The same conditions were also applicable only dicyanobenzoquinone in the presence of n-Bu4NN3 is a useful for monocarboxylic acids with electron donor groups system for efficient conversion of tetrahydropyranyl (THP) due to the high nucleophilicity of their carboxylate ethers to their corresponding alkyl azides. Phosphorus, Sul- ions. fur, and Silicon and the Related Elements, 180, 1601–1604. To further study the proposed mechanism, and to DOI: 10.1080/104265090884292. Akhlaghinia, B. (2005b). A new and convenient method find the influence of PPh3, the reaction was carried out of generating alkyl isocyanates from alcohols, thiols and in the absence of PPh3. Neither carboxylic anhydride trimethylsilyl ethers using triphenylphosphine/2,3-dichloro- as the product nor acyl chloride as the by-product was Author5,6-dicyanobenzoquinone/Bu copy4 NOCN. Synthesis, 2005, 1955– obtained. The fact that no reaction occurs without 1958. DOI: 10.1055/s-2005-869906. PPh3 suggests that TCCA acts as a carboxyl group Akhlaghinia, B., & Samiei, S. (2009). Triphenylphosphine/2,3- activator only in the presence of PPh3. dichloro-5,6-dicyanobenzoquinone (DDQ)/[n-Bu4N]OCN as Also, the reaction was carried out in the absence a useful system for the efficient conversion of tetrahydropy- of potassium carboxylate ions to find any carboxylic ranyl (THP) ethers to the corresponding alkyl isocyanates. Phosphorus, Sulfur, and Silicon and the Related Elements, acid chlorides species formed as intermediates or by- 184, 2525–2529. DOI: 10.1080/10426500802508212. products of carboxylic acids transformation to their Akhlaghinia, B., & Rouhi-Saadabad, H. (2013). 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