DOCSLIB.ORG

Chapter 16. Aldehydes and Ketones: Nucleophilic Addition Reactions

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Chapter 16. Aldehydes and Ketones: Nucleophilic Addition Reactions Chapter 16. Aldehydes and Ketones: Nucleophilic Addition Reactions Based on McMurry’s Organic Chemistry, 7th edition Aldehydes and Ketones Aldehydes (RCHO) and ketones (R2CO) are characterized by the the carbonyl functional group (C=O) The compounds occur widely in nature as intermediates in metabolism and biosynthesis 2 Why this Chapter? Much of organic chemistry involves the chemistry of carbonyl compounds Aldehydes/ketones are intermediates in synthesis of pharmaceutical agents, biological pathways, numerous industrial processes An understanding of their properties is essential 3 19.1 Naming Aldehydes and Ketones Aldehydes are named by replacing the terminal -e of the corresponding alkane name with –al The parent chain must contain the CHO group The CHO carbon is numbered as C1 If the CHO group is attached to a ring, use the suffix carbaldehyde. See Table 19.1 for common names 4 Naming Ketones Replace the terminal -e of the alkane name with –one Parent chain is the longest one that contains the ketone group Numbering begins at the end nearer the carbonyl carbon 5 Ketones with Common Names IUPAC retains well-used but unsystematic names for a few ketones 6 Ketones and Aldehydes as Substituents The R–C=O as a substituent is an acyl group, used with the suffix -yl from the root of the carboxylic acid CH3CO: acetyl; CHO: formyl; C6H5CO: benzoyl The prefix oxo- is used if other functional groups are present and the doubly bonded oxygen is labeled as a substituent on a parent chain 7 19.2 Preparation of Aldehydes and Ketones Preparing Aldehydes Oxidize primary alcohols using pyridinium chlorochromate Alkenes with a vinylic hydrogen can undergo oxidative cleavage when treated with ozone, yielding aldehydes Reduce an ester with diisobutylaluminum hydride (DIBAH) 8 Preparing Ketones Oxidize a 2° alcohol Many reagents possible: choose for the specific situation (scale, cost, and acid/base sensitivity) 9 Ketones from Ozonolysis Ozonolysis of alkenes yields ketones if one of the unsaturated carbon atoms is disubstituted 10 Aryl Ketones by Acylation Friedel–Crafts acylation of an aromatic ring with an acid chloride in the presence of AlCl3 catalyst 11 Methyl Ketones by Hydrating Alkynes Hydration of terminal alkynes in the presence of Hg2+ (catalyst: Section 8.4) 12 19.3 Oxidation of Aldehydes and Ketones CrO3 in aqueous acid oxidizes aldehydes to carboxylic acids efficiently at room temperature in good yield Silver oxide, Ag2O, in aqueous ammonia (Tollens’ reagent) oxidizes aldehydes without harming carbon-carbon double bond or other acidic- sensitive functional groups in a molecule 13 Hydration of Aldehydes Aldehyde oxidations occur through 1,1-diols (“hydrates”) Reversible addition of water to the carbonyl group Aldehyde hydrate is oxidized to a carboxylic acid by usual reagents for alcohols 14 Ketones Oxidize with Difficulty Undergo slow cleavage with hot, alkaline KMnO4 C–C bond next to C=O is broken to give carboxylic acids Reaction is practical for cleaving symmetrical ketones Product mixtures are formed from unsymmetrical ketones. 15 19.4 Nucleophilic Addition Reactions of Aldehydes and Ketones Nu- approaches 75° to the plane of C=O and adds to C A tetrahedral alkoxide ion intermediate is produced 16 Nucleophiles Nucleophiles can be negatively charged ( : Nu) or neutral ( : Nu) at the reaction site The overall charge on the nucleophilic species is not considered 17 Nucleophilic Addition Reactions of Aldehydes and Ketones The general reaction pathways of Nucleophilic Addition Reactions of Aldehydes and Ketones ,leads to an alcohol product or the product with a C= Nu bund. 18 Relative Reactivity of Aldehydes and Ketones Aldehydes are generally more reactive than ketones in nucleophilic addition reactions The transition state for addition is less congested and lower in energy for an aldehyde (a) than for a ketone (b) Aldehydes have one large substituent bonded to the C=O: ketones have two Electronically, aldehydes are more reactive than ketones because of the greater polarization of aldehyde carbonyl groups. 19 Electrophilicity of Aldehydes and Ketones Aldehyde C=O is more polarized than ketone C=O As in carbocations, more alkyl groups stabilize + character Ketone has more alkyl groups, stabilizing the C=O carbon inductively 20 Reactivity of Aromatic Aldehydes Aromatic aldehydes Less reactive in nucleophilic addition reactions than aliphatic aldehydes Electron-donating resonance effect of aromatic ring makes C=O less reactive electrophile than the carbonyl group of an aliphatic aldehyde 21 19.5 Nucleophilic Addition of H2O: Hydration Aldehydes and ketones react with water to yield 1,1- diols Hyrdation is reversible: a diol can eliminate water 22 Base-Catalyzed Addition of Water Addition of water is catalyzed by both acid and base The base-catalyzed hydration nucleophile is the hydroxide ion, which is a much stronger nucleophile than water 23 Acid-Catalyzed Addition of Water Protonation of C=O makes it more electrophilic 24 Addition of H-Y to C=O Reaction of C=O with H-Y, where Y is electronegative, gives an addition product (“adduct”) Formation is readily reversible and does not normally lead to a stable alcohol addition product. 25 19.6 Nucleophilic Addition of HCN: Cyanohydrin Formation Aldehydes and unhindered ketones react with HCN to yield cyanohydrins, RCH(OH)CN Addition of HCN is reversible and base-catalyzed, generating nucleophilic cyanide ion, CN- as KCN Addition of CN to C=O yields a tetrahedral intermediate, which is then protonated Equilibrium favors adduct 26 Uses of Cyanohydrins The nitrile group (CN) can be reduced with LiAlH4 to yield a primary amine (RCH2NH2) Can be hydrolyzed by hot acid to yield a carboxylic acid 27 19.7 Nucleophilic Addition of Grignard Reagents and Hydride Reagents: Alcohol Formation Treatment of aldehydes or ketones with Grignard reagents yields an alcohol Nucleophilic addition of the equivalent of a carbon anion, or carbanion. A carbon–magnesium bond is strongly polarized, so a Grignard reagent reacts for all practical purposes as R : MgX +. 28 Mechanism of Addition of Grignard Reagents Complexation of C=O by Mg2+, Nucleophilic addition of R : , protonation by dilute acid yields the neutral alcohol Grignard additions are irreversible because a carbanion is not a leaving group 29 Hydride Addition Convert C=O to CH-OH LiAlH4 and NaBH4 react as donors of hydride ion Protonation after addition yields the alcohol 30 19.8 Nucleophilic Addition of Amines: Imine and Enamine Formation RNH2 adds to C=O to form imines, R2C=NR (after loss of HOH) R2NH yields enamines, R2NCR=CR2 (after loss of HOH) (ene + amine = unsaturated amine) 31 Imine Derivatives Addition of amines with an atom containing a lone pair of electrons on the adjacent atom occurs very readily, giving useful, stable imines For example, hydroxylamine forms oximes and 2,4- dinitrophenylhydrazine readily forms 2,4- dinitrophenylhydrazones These are usually solids and help in characterizing liquid ketones or aldehydes by melting points 32 33 19.9 Nucleophilic Addition of Hydrazine: The Wolff–Kishner Reaction Treatment of an aldehyde or ketone with hydrazine, H2NNH2 and KOH converts the compound to an alkane Originally carried out at high temperatures but with dimethyl sulfoxide as solvent takes place near room temperature 34 19.10 Nucleophilic Addition of Alcohols: Acetal Formation Alcohols are weak nucleophiles but acid promotes addition forming the conjugate acid of C=O Addition yields a hydroxy ether, called a hemiacetal (reversible); further reaction can occur 35 Uses of Acetals Reduce only the ester group of ethyl 4-oxopentanoate, If Treatment of the starting keto ester with LiALH4 would reduce both the keto and the ester groups to give a diol product. 36 For that ,the first converting the keto group to an acetal, then reducing the ester with LiAlH4,and then removing the acetal by treatment with aqueous acid. 37 19.11 Nucleophilic Addition of Phosphorus Ylides: The Wittig Reaction The sequence converts C=O is to C=C A phosphorus ylide adds to an aldehyde or ketone to yield a dipolar intermediate called a betaine The intermediate spontaneously decomposes through a four-membered ring to yield alkene and triphenylphosphine oxide, (Ph)3P=O Formation of the ylide is shown below 38 The mechanism of Witting reaction Aldehydes and ketones are Converted into alkene By this reaction. 39 Uses of the Wittig Reaction Can be used for monosubstituted, disubstituted, and trisubstituted alkenes but not tetrasubstituted alkenes The reaction yields a pure alkene of defined structure with methylenetriphenylphosphorane For comparison, addition of CH3MgBr to cyclohexanone and dehydration with, yields a mixture of two alkenes 40 19.13 Conjugate Nucleophilic Addition to -Unsaturated Aldehydes and Ketones A nucleophile can add to the C=C double bond of an ,- unsaturated aldehyde or ketone . The initial product is a resonance- stabilized enolate ion, which is then protonated 41 Conjugate Addition of Amines Primary and secondary amines add to , - unsaturated aldehydes and ketones to yield -amino aldehydes and ketones 42 Conjugate Addition of Alkyl Groups: Organocopper Reactions Conjugate addition of an alkyl group to an , - unsaturated ketone (but not aldehyde) is more useful by Grignard regent Or addition of an alkyl to an , -unsaturated ketone Group is by Gilman reagent (1 equivalent of cuprous iodide and 2 equvalents of organolithium) 43 Conjugate Addition of Alkyl Groups: Organocopper Reactions 1, 2, 3 alkyl, aryl and alkenyl groups react but not alkynyl groups 44 Mechanism of Alkyl Conjugate Addition Conjugate nucleophilic addition of a diorganocopper anion, R2Cu , to an enone Transfer of an R group and elimination of a neutral organocopper species, RCu 45.
Load more

Recommended publications
  • Nucleophilic Aromatic Substitution
    NUCLEOPHILIC AROMATIC SUBSTITUTION Ms. Prerana Sanas M.Pharm (Pharmceutical Chemistry) Asst.Professor, NCRD’s Sterling Institute of Pharmacy Nerul Navi Mumbai Nucleophilic aromatic substitution results in the substitution of a halogen X on a benzene ring by a nucleophile (:Nu– ). Aryl halides undergo a limited number of substitution reactions with strong nucleophiles. NAS occurs by two mechanisms i) Bimoleccular displacement (Addition –Elimination) ii) Benzyne Formation( Elimination –Addition) 7/5/2019 Ms.Prerana Sanas 2 Bimolecular displacement (Addition – Elimination) Aryl halides with strong electron-withdrawing groups (such as NO2) on the ortho or para positions react with nucleophiles to afford substitution products. For example, treatment of p-chloronitrobenzene with hydroxide (– OH) affords p-nitrophenol by replacement of Cl by OH. Nucleophilic aromatic substitution occurs with a variety of strong nucleophiles, including – OH, – OR, – NH2, – SR, and in some cases, neutral nucleophiles such as NH3 and RNH2 . 7/5/2019 Ms.Prerana Sanas 3 Mechanism…… The mechanism of these reactions has two steps: Step i) Addition of the nucleophile (:Nu– ) forms a resonance-stabilized carbanion with a new C – Nu bond—three resonance structures can be drawn. • Step [1] is rate-determining since the aromaticity of the benzene ring is lost. In Step ii) loss of the leaving group re-forms the aromatic ring. This step is fast because the aromaticity of the benzene ring is restored. 7/5/2019 Ms.Prerana Sanas 4 Factors affecting Bimolecular displacement Increasing the number of electron-withdrawing groups increases the reactivity of the aryl halide. Electron-withdrawing groups stabilize the intermediate carbanion, and by the Hammond postulate, lower the energy of the transition state that forms it.
    [Show full text]
  • SAFETY DATA SHEET Isopropyl Alcohol
    SAFETY DATA SHEET Isopropyl Alcohol Section 1. Identification GHS product identifier : Isopropyl Alcohol Chemical name : Isopropyl alcohol Other means of : isopropanol; 2-Propanol identification Product type : Liquid. Product use : Synthetic/Analytical chemistry. Synonym : isopropanol; 2-Propanol SDS # : 001105 Supplier's details : Airgas USA, LLC and its affiliates 259 North Radnor-Chester Road Suite 100 Radnor, PA 19087-5283 1-610-687-5253 24-hour telephone : 1-866-734-3438 Section 2. Hazards identification OSHA/HCS status : This material is considered hazardous by the OSHA Hazard Communication Standard (29 CFR 1910.1200). Classification of the : FLAMMABLE LIQUIDS - Category 2 substance or mixture EYE IRRITATION - Category 2A SPECIFIC TARGET ORGAN TOXICITY (SINGLE EXPOSURE) (Narcotic effects) - Category 3 GHS label elements Hazard pictograms : Signal word : Danger Hazard statements : May form explosive mixtures with air. Highly flammable liquid and vapor. Causes serious eye irritation. May cause drowsiness or dizziness. Precautionary statements General : Read label before use. Keep out of reach of children. If medical advice is needed, have product container or label at hand. Prevention : Wear protective gloves. Wear eye or face protection. Keep away from heat, hot surfaces, sparks, open flames and other ignition sources. No smoking. Use explosion- proof electrical, ventilating, lighting and all material-handling equipment. Use only non- sparking tools. Take precautionary measures against static discharge. Keep container tightly closed. Use only outdoors or in a well-ventilated area. Avoid breathing vapor. Wash hands thoroughly after handling. Response : IF INHALED: Remove person to fresh air and keep comfortable for breathing. Call a POISON CENTER or physician if you feel unwell.
    [Show full text]
  • Lecture 5 Diastereoselective Addition Into Carbonyl Compounds
    Lecture 5 Diastereoselective Addition into Carbonyl Compounds Containing α-Stereogenic Centres Learning outcomes: by the end of this lecture, and after answering the associated problems, you will be able to: 1. use the Felkin-Anh T.S. to predict the stereochemical outcome of reactions carried out on carbonyl compounds that possess an α-stereogenic centre; 2. rationalise the preferential adoption of a Felkin-Anh T.S. in nucleophilic addition reactions on steric and stereoelectronic grounds; 3. understand how the presence of an α-electron-withdrawing substituent affects the Felkin-Anh T.S.; 4. use the Felkin-Anh T.S. to prepare 1,2-syn diols from α-alkoxy ketones; 5. use the Cram chelation model to prepare 1,2-anti diols from α-alkoxy ketones. Stereoselective Addition of Nucleophiles into Ketones and Aldehydes containing α- Stereogenic Centres The addition of a nucleophile into a chiral ketone or aldehyde provides diastereoisomers. When the stereogenic centres in the substrate are close to the reacting carbonyl group (e.g. 1,2-disposed), then it is often possible to exploit this stereochemical information to control the stereoselectivity of the addition reaction. This method for controlling the stereochemical outcome of a reaction is known as substrate control. A number of models have been developed for predicting the stereochemical outcome of this type of reaction. Felkin-Anh Model Consider a carbonyl compound containing an α-stereogenic centre in which the three substituents at the α-site are well differentiated in size: O HO Nu Nu OH RL Nu RL RL R R R S M S M S RM R R R R R RS = small substituent RM = medium-sized substituent RL = large substituent Of the two diastereoisomeric alcohol addition products, one will be formed to a greater extent than the other.
    [Show full text]
  • N-BUTYL ALCOHOL
    Right to Know Hazardous Substance Fact Sheet Common Name: n-BUTYL ALCOHOL Synonyms: Propyl Carbinol; n-Butanol CAS Number: 71-36-3 Chemical Name: 1-Butanol RTK Substance Number: 1330 Date: November 1998 Revision: January 2008 DOT Number: UN 1120 Description and Use EMERGENCY RESPONDERS >>>> SEE BACK PAGE n-Butyl Alcohol is a colorless liquid with a strong, sweet Hazard Summary alcohol odor. It is used as a solvent for fats, waxes, shellacs, Hazard Rating NJDOH NFPA resins, gums, and varnish, in making hydraulic fluids, and in HEALTH - 2 medications for animals. FLAMMABILITY - 3 REACTIVITY - 0 f ODOR THRESHOLD = 1 to 15 ppm FLAMMABLE f Odor thresholds vary greatly. Do not rely on odor alone to POISONOUS GASES ARE PRODUCED IN FIRE determine potentially hazardous exposures. CONTAINERS MAY EXPLODE IN FIRE Hazard Rating Key: 0=minimal; 1=slight; 2=moderate; 3=serious; Reasons for Citation 4=severe f n-Butyl Alcohol is on the Right to Know Hazardous f n-Butyl Alcohol can affect you when inhaled and by Substance List because it is cited by OSHA, ACGIH, DOT, passing through the skin. NIOSH, DEP, IRIS, NFPA and EPA. f Contact can irritate and burn the skin. f This chemical is on the Special Health Hazard Substance f n-Butyl Alcohol can irritate and burn the eyes with possible List. eye damage. f Inhaling n-Butyl Alcohol can irritate the nose, throat and lungs. f Exposure to n-Butyl Alcohol can cause headache, dizziness, nausea and vomiting. SEE GLOSSARY ON PAGE 5. f n-Butyl Alcohol can damage the liver, kidneys, hearing, and sense of balance.
    [Show full text]
  • Williamson Ether Synthesis the Williamson Ether Synthesis Is an Organic Reaction, Forming an Ether from an Alkyl Halide and an Alcohol
    The Williamson ether synthesis The Williamson ether synthesis is an organic reaction, forming an ether from an alkyl halide and an alcohol. This reaction was developed by Alexander Williamson in 1850. It involves the reaction of an alkoxide ion with a primary alkyl halide via an SN2 reaction. The Williamson reaction is widely used in both laboratory and industrial synthesis, and remains the simplest and most popular method of preparing ethers. Both symmetrical and asymmetrical ethers are easily prepared. The reaction for this week: an example of a Williamson ether synthesis acetaminophen ethyl iodide phenacetin starting material reagent product Phenacetin may be synthesized as an example of the Williamson ether synthesis The first synthesis of phenacetin was reported in 1878 by Harmon Morse. Procedure 1. Weigh an Extra-Strength Tylenol tablet. Pulverize the tablet with mortar and pestle. Weigh out 0.22 g and place it in a dry 15-ml round-bottom flask along with 0.28 g of finely pulverized K2CO3 (mortar and pestle) and 3.0 mL of butanone. Carefully add 0.28 mL of ethyl iodide with a syringe. 2. Add a stir bar; attach a microscale water-cooled condenser to the flask. Heat the mixture under reflux directly on a hot plate at medium setting for 1 hour. In the meantime, obtain the IR of acetaminophen. 3. Turn off the heat. Allow the mixture to cool down. Add 4 mL of water to the flask and transfer its contents to a 16 x 125 mm test tube with a screw cap. Rinse round-bottom flask 4 times with 1 mL of tert-butyl methyl ether (BME) and add the rinsings to the test tube.
    [Show full text]
  • Ketenes 25/01/2014 Part 1
    Baran Group Meeting Hai Dao Ketenes 25/01/2014 Part 1. Introduction Ph Ph n H Pr3N C A brief history Cl C Ph + nPr NHCl Ph O 3 1828: Synthesis of urea = the starting point of modern organic chemistry. O 1901: Wedekind's proposal for the formation of ketene equivalent (confirmed by Staudinger 1911) Wedekind's proposal (1901) 1902: Wolff rearrangement, Wolff, L. Liebigs Ann. Chem. 1902, 325, 129. 2 Wolff adopt a ketene structure in 1912. R 2 hν R R2 1905: First synthesis and characterization of a ketene: in an efford to synthesize radical 2, 1 ROH R C Staudinger has synthesized diphenylketene 3, Staudinger, H. et al., Chem. Ber. 1905, 1735. N2 1 RO CH or Δ C R C R1 1907-8: synthesis and dicussion about structure of the parent ketene, Wilsmore, O O J. Am. Chem. Soc. 1907, 1938; Wilsmore and Stewart Chem. Ber. 1908, 1025; Staudinger and Wolff rearrangement (1902) O Klever Chem. Ber. 1908, 1516. Ph Ph Cl Zn Ph O hot Pt wire Zn Br Cl Cl CH CH2 Ph C C vs. C Br C Ph Ph HO O O O O O O O 1 3 (isolated) 2 Wilsmore's synthesis and proposal (1907-8) Staudinger's synthesis and proposal (1908) wanted to make Staudinger's discovery (1905) Latest books: ketene (Tidwell, 1995), ketene II (Tidwell, 2006), Science of Synthesis, Vol. 23 (2006); Latest review: new direactions in ketene chemistry: the land of opportunity (Tidwell et al., Eur. J. Org. Chem. 2012, 1081). Search for ketenes, Google gave 406,000 (vs.
    [Show full text]
  • How Is Alcohol Metabolized by the Body?
    Overview: How Is Alcohol Metabolized by the Body? Samir Zakhari, Ph.D. Alcohol is eliminated from the body by various metabolic mechanisms. The primary enzymes involved are aldehyde dehydrogenase (ALDH), alcohol dehydrogenase (ADH), cytochrome P450 (CYP2E1), and catalase. Variations in the genes for these enzymes have been found to influence alcohol consumption, alcohol-related tissue damage, and alcohol dependence. The consequences of alcohol metabolism include oxygen deficits (i.e., hypoxia) in the liver; interaction between alcohol metabolism byproducts and other cell components, resulting in the formation of harmful compounds (i.e., adducts); formation of highly reactive oxygen-containing molecules (i.e., reactive oxygen species [ROS]) that can damage other cell components; changes in the ratio of NADH to NAD+ (i.e., the cell’s redox state); tissue damage; fetal damage; impairment of other metabolic processes; cancer; and medication interactions. Several issues related to alcohol metabolism require further research. KEY WORDS: Ethanol-to­ acetaldehyde metabolism; alcohol dehydrogenase (ADH); aldehyde dehydrogenase (ALDH); acetaldehyde; acetate; cytochrome P450 2E1 (CYP2E1); catalase; reactive oxygen species (ROS); blood alcohol concentration (BAC); liver; stomach; brain; fetal alcohol effects; genetics and heredity; ethnic group; hypoxia The alcohol elimination rate varies state of liver cells. Chronic alcohol con- he effects of alcohol (i.e., ethanol) widely (i.e., three-fold) among individ- sumption and alcohol metabolism are on various tissues depend on its uals and is influenced by factors such as strongly linked to several pathological concentration in the blood T chronic alcohol consumption, diet, age, consequences and tissue damage. (blood alcohol concentration [BAC]) smoking, and time of day (Bennion and Understanding the balance of alcohol’s over time.
    [Show full text]
  • Phosphine-Catalyzed Additions of Nucleophiles and Electrophiles to Α
    PHOSPHINE-CATALYZED ADDITIONS OF NUCLEOPHILES AND ELECTROPHILES TO α,β–UNSATURATED CARBONYL COMPOUNDS Reported by Michael Scott Bultman November 4, 2004 INTRODUCTION Organophosphorous compounds are becoming increasingly important in organic synthesis. Phosphines serve as precursors to phosphonium ylides in the Wittig reaction,1 and as nucleophilic triggers in the Mitsunobu2 and Staudinger3 reactions. In these processes, the phosphine is stoichiometrically consumed and converted into a phosphine oxide. Phosphines are also commonly used as ligands for transition metal-catalyzed reactions, to modulate reactivity and stereocontrol.4 On the other hand, the use of phosphines as nucleophilic catalysts for organic reactions has only gained attention in the last ten years. First reported by Rauhut and Currier in 1963,5 phosphine catalysis has since been reinvestigated after the phosphine ligands in some transition-metal-catalyzed reactions were found to be better catalysts than the metal/phosphine complexes alone!6 Phosphines are well suited for catalyzing the addition of both nucleophiles and electrophiles to electron deficient alkenes, alkynes, and allenes. Activation of these α,β-unsaturated carbonyl systems with the phosphine enables the formation of new bonds at the α-, β-, and γ-positions. This report will highlight these different modes of addition to α,β-unsaturated carbonyl systems under phosphine catalysis that allow for the formation of a wide array of products from a single class of substrates. GENERAL REACTIVITY OF PHOSPHINES Key characteristics required for successful nucleophilic catalysis lie in the balance of leaving group ability, nucleophilicity, and ease of ylid formation. Increasing leaving group ability can often be + correlated with decreasing basicity.
    [Show full text]
  • Sugar Alcohols—Their Role in the Modern World of Sweeteners: a Review
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Springer - Publisher Connector Eur Food Res Technol (2015) 241:1–14 DOI 10.1007/s00217-015-2437-7 REVIEW PAPER Sugar alcohols—their role in the modern world of sweeteners: a review Małgorzata Grembecka Received: 31 August 2014 / Revised: 16 December 2014 / Accepted: 13 February 2015 / Published online: 28 February 2015 © The Author(s) 2015. This article is published with open access at Springerlink.com Abstract Epidemic obesity and diabetes encouraged the observed. It was mainly due to the developments in bio- changes in population lifestyle and consumers’ food prod- logical studies, the change of a population lifestyle and the ucts awareness. Food industry has responded people’s increase in the consumer awareness concerning food prod- demand by producing a number of energy-reduced prod- ucts. The health quality of food depends mainly on nutri- ucts with sugar alcohols as sweeteners. These compounds ents, but also on foreign substances such as food additives. are usually produced by a catalytic hydrogenation of carbo- The presence of foreign substances in the food can be justi- hydrates, but they can be also found in nature in fruits, veg- fied, allowed or tolerated only when they are harmless to etables or mushrooms as well as in human organism. Due our health. Epidemic obesity and diabetes encouraged the to their properties, sugar alcohols are widely used in food, growth of the artificial sweetener industry. There are more beverage, confectionery and pharmaceutical industries and more people who are trying to lose weight or keeping throughout the world.
    [Show full text]
  • Aromatic Nucleophilic Substitution Reaction
    Aromatic Nucleophilic Substitution Reaction DR. RAJENDRA R TAYADE ASSISTANT PROFESSOR DEPARTMENT OF CHEMISTRY INSTITUTE OF SCIENCE, NAGPUR Principles There are four principal mechanisms for aromatic nucleophilic substitution which are similar to that of aliphatic nucleophilic substitution. (SN1, SN2, SNi, SET Mechanism) 1. SNAr Mechanism- addition / elimination CF3, CN, CHO, COR, COOH, Br, Cl, I Common Activating Groups for NAS Step [1] Addition of the nucleophile (:Nu–) to form a carbanion Addition of the nucleophile (:Nu–) forms a resonance-stabilized carbanion with a new C – Nu bond— three resonance structures can be drawn. • Step is rate-determining • Aromaticity of the benzene ring is lost Step [2] loss of the leaving group re-forms the aromatic ring. • This step is fast because the aromaticity of the benzene ring is restored. ? Explain why a methoxy group (CH3O) increases the rate of electrophilic aromatic substitution, but decreases the rate of nucleophilic aromatic substitution. 2.ArSN1 Mechanism- elimination /addition • This mechanism operates in the reaction of diazonium salts with nucleophiles. •The driving force resides in the strength of the bonding in the nitrogen molecule that makes it a particularly good leaving group. 3.Benzyne Mechanism- elimination /addition Step [1] Elimination of HX to form benzyne Elimination of H and X from two adjacent carbons forms a reactive benzyne intermediate Step [2] Nucleophilic addition to form the substitution product Addition of the nucleophile (–OH in this case) and protonation form the substitution product Evidence for the Benzyne Mechanism Trapping in Diels/Alder Reaction O O B E N Z Y N E C C O O O D i e l s / A l d e r O N H 3 N N Dienophile Diene A d d u c t Substrate Modification – absence of a hydrogens LG Substituent Substituent No Reaction Base Isotopic Labeling LG Nu H Nu Structure of Benzyne • The σ bond is formed by overlap of two sp2 hybrid orbitals.
    [Show full text]
  • Core Alcohol and Drug Survey
    Form 194 Core Alcohol and Drug Survey For additional use: Long Form A 0 1 2 3 4 5 6 7 8 9 B 0 1 2 3 4 5 6 7 8 9 FIPSE Core Analysis Grantee Group Core Institute C 0 1 2 3 4 5 6 7 8 9 Student Health Programs 0 1 2 3 4 5 6 7 8 9 Southern Illinois University D Please use a number 2 Pencil. Carbondale, IL 62901 E 0 1 2 3 4 5 6 7 8 9 1. Classification: 2. Age: 3. Ethnic origin: 4. Marital status: Freshman . American Indian/ Single . Sophomore . Alaskan Native . Married . Junior . 0 0 Hispanic . Separated . Senior. 1 1 Asian/Pacific Islander . Divorced. Grad/professional . 2 2 White (non-Hispanic) . Widowed . Not seeking a 3 3 Black (non-Hispanic) . degree . 4 4 Other . 7. Are you working? Other . 5 5 Ye s, full-time . 6 6 6. Is your current residence Ye s, part-time . 5. Gender: 7 7 as a student: No . Male . 8 8 On-campus . Female . 9 9 Off-campus . 8. Living arrangements: A. Where: (mark best answer) 9. Approximate cumulative grade point average: (choose one) House/apartment/etc. Residence hall . A+AA- B+BB- C+CC- D+DD-F Approved housing. Fraternity or sorority . 10. Some students have indicated that alcohol or drug use at parties they attend in and Other . around campus reduces their enjoyment, often leads to negative situations, and therefore, they would rather not have alcohol and drugs available and used. Other B. With whom: students have indicated that alcohol and drug use at parties increases their (mark all that apply) enjoyment, often leads to positive situations, and therefore, they would rather have With roommate(s).
    [Show full text]
  • Sugar Alcohols: a Review
    International Journal of PharmTech Research CODEN (USA): IJPRIF, ISSN: 0974-4304, ISSN(Online): 2455-9563 Vol.9, No.7, pp 407-413, 2016 Sugar alcohols: A review Ramezan Ali Mahian1, Vahid Hakimzadeh2* 1,2Department of Food Science and Technology, Quchan Branch, Islamic Azad University, Quchan, Iran Abstract : Sugar alcohols are extensively used as sweetening agents. They sometimes possess advantages over the parent sugars in sweetness, caloric reduction and non-cariogenicity. The physical status of carbohydrates in food and confectionery affects both the properties of the product during production and the quality of the final product. Sugar alcohols, such as xylitol, mannitol, sorbitol, and erythritol are emerging food ingredients that provide similar or better sweetness/sensory properties of sucrose, but are less calorigenic. Also, sugar alcohols can be converted into commodity chemicals through chemical catalysis. Biotechnological production offers the safe and sustainable supply of sugar alcohols from renewable biomass. These compounds are usually produced by a catalytic hydrogenation of carbohydrates, but they can be also found in nature in fruits, vegetables or mushrooms as well as in human organism. Due to their properties, sugar alcohols are widely used in food, beverage, confectionery and pharmaceutical industries throughout the world. They have found use as bulk sweeteners that promote dental health and exert prebiotic effect. They are added to foods as alternative sweeteners what might be helpful in the control of calories intake. Consumption of low-calorie foods by the worldwide population has dramatically increased, as well as health concerns associated with the consequent high intake of sweeteners. Key words: Sugar alcohols, low-calorie, Sugar-free products, sweetener.
    [Show full text]