2-chloroethyl bromoethanoate from ethanol and/or ethanoic acid Other Acylation Reagents and Techniques Because acylation is such an important and widely used transformation, the general reactions described above have been supplemented by many novel procedures and reagents that accomplish similar overall change. c. \(\ce{CH_3CH_3COC(CH_3)_2CON(CH_3)_2}\) g. 2,2-dimethylpropyl 2,2-dimethylpropanoate from tert-butyl chloride. Reaction of 3º-amines with strong acylating reagents may generate acylammonium species reversibly (see below), but these are as reactive as acyl chlorides and will have only a very short existence. A mechanism will be shown above by clicking on the diagram. Exercise 18-14 Explain why decarboxylation of 2,2-dimethyl-3-oxobutanoic acid, \(\ce{CH_3COC(CH_3)_2CO_2H}\), in the presence of bromine gives 3-methyl-3-bromo-2-butanone, \(\ce{CH_3COC(CH_3)_2Br}\). Because of these differences, the conversion of one type of acid derivative into another is generally restricted to those outlined in the following diagram. Complete the steps necessary to give all of the products and regenerate the catalyst. f. \(\ce{CH_3COCl} + 2 \ce{NH_3} \rightarrow \ce{CH_3CONH_2} + \ce{NH_4Cl}\) How could this difference in bond lengths tend to compensate for the differences in electronegativity between chlorine and fluorine and make the acids similar in strength? Exercise 18-38 Why does the following reaction fail to give ethyl propanoate? Give your reasoning. Colourless crystalline compound. c. \(\ce{CH_3CO_2O} + \ce{CH_3OH} \overset{\ce{H}^\oplus}{\longrightarrow} \ce{CH_3CO_2CH_3} + \ce{CH_3CO_2H}\) Legal. l. \(\ce{C_6H_5CH=CH-CH(OH)CH_2CO_2C_2H_5}\). e.g. h. 171ºC soluble in water, alcohol, insoluble in ether. b. Here, it was noted that amino groups were strongly electron donating (resonance effect >> inductive effect), alkoxy groups were slightly less activating, acyloxy groups still less activating (resonance effect > inductive effect) and chlorine was deactivating (inductive effect > resonance effect). Base catalyzed hydrolysis produces carboxylate salts. Furthermore, electronic and steric factors are also important to consider when comparing reactivities of carboxylic acids and their derivatives. No acylation reactions of amides were shown in these problems. The acidity of carboxylic acids and 1º & 2º-amides acts to convert Grignard and alkyl lithium reagents to hydrocarbons (see equations), so these functional groups should be avoided when these reagents are used. (Review Section 17-1. Exercise 18-15 What information would you need to calculate \(\Delta H^0\) for the reaction \(\ce{CH_3CO_2} \cdot \rightarrow \ce{CO_2} + \cdot \ce{CH_3}\)? If no change the acid is 1, 8 or more. Carboxylic acids. Methods for converting carboxylic acids into these derivatives were shown in a previous section, but the amide and anhydride preparations were not general and required strong heating. Examples of these reductions are provided in the following diagram. How could you use an \(\ce{N}\),\(\ce{N}\)-dialkylalkanamide to prepare an aldehyde with the aid of a Grignard reagent? : On heating the acid with acetic anhydride and then distilling the product at 300ºC, 1, 4 and 1, 5 - dicarboxylic acid give cyclic anhydrides and 1, 6 and 1, 7-dicarboxylic acid give cyclic ketones provided the acids are unsubstituted. \(\ce{CH_3CH_2COCH(CH_3)CH_2CH_2CH(CH_3)_2}\) (Section 17-4A. Note that LAH is the strongest reducing agent listed, and it reduces all the substrates. By using a platinum catalyst and increased temperature and pressure, it is possible to reduce aldehydes and ketones to alcohols, but carboxylic acids, esters and amides are comparatively unreactive. In principle all steps are reversible, but in practice many reactions of this kind are irreversible unless changes in the reactants and conditions are made. They are made from carboxylic acids by this reaction (Atkins & Carey, Sec 12:10): In the mechanism we just looked at, the key steps (attack of a nucleophile and departure of a leaving group) were accompanied by steps in which protons moved from one location to another. Write appropriate mechanisms to explain these facts. Cyclic esters are called lactones.   (i) catalytic hydrogenation \(\ce{CH_3CH_2CH_2CH(CH_2CH=CH_2)CO_2H}\) EDC Amide formation mechanism from carboxylic acid and amine, DCC Amide formation mechanism from carboxylic acid and amine, The Mechanism of Organolithium Reaction with Nitriles, The Mechanism of Nitrile Reduction to 1o Amine with LiAlH4, The Mechanism of Nitrile Reduction to Aldehyde with DIBAL, The Mechanism of Base-Catalyzed Hydrolysis of Nitriles, The Mechanism of Acid-Catalyzed Hydrolysis of Nitriles, The Mechanism of Amide Reduction to Amine by LiAlH4- short version, The Mechanism of Amide Reduction to Amine by LiAlH4, The Mechanism of Amide Dehydration to Nitrile with SOCl2, The Mechanism of Amide Dehydration to Nitrile with POCl3, The Mechanism of Amide Dehydration to Nitrile with P2O5, The Mechanism of Acid-Catalyzed Amide Hydrolysis, Mechanism of Base-Catalyzed Amide Hydrolysis, Amide Reactions Summary - Hydrolysis, Reduction, Dehydration, The Mechanism of Grignard Reaction with Anhydrides. Stronger than aliphatic acids and sparingly soluble in water. Exercise 18-46 Would you expect 3-butenoic acid to form a lactone with a five- or a four-membered ring when heated with a catalytic amount of sulfuric acid? Natural tartaric acid is d-tartaric acid. Give your reasoning. j. Explain why the acyl cation, \(11\) of 2,4,6-trimethylbenzoic acid might be more stable, relative to the conjugate acid of benzoic acid. The acids obtained by replacing one or more hydrogen atoms from the alkyl group of the acid by groups such as Cl, OH, CN, NH. Grignard reagents add to nitriles, forming a relatively stable imino derivative which can be hydrolyzed to a ketone. a. ethyl 2-methyl-3-oxopentanoate from ethyl propanoate The following table lists some representative derivatives and their boiling points. g. \(\ce{CH_3CO_2CH_3} + \ce{CH_3NH_2} \rightarrow \ce{CH_3CONHCH_3} + \ce{CH_3OH}\). Amides are very polar, thanks to the n-π conjugation of the nitrogen non-bonded electron pair with the carbonyl group. CARBOXYLIC ACIDS AND THEIR DERIVATIVES The compounds containing the carboxyl functional group are called Carboxylic acids. Explain. Reduction occurs very slowly or not at all (N.R. \(\ce{HCO_2H}\) and \(\ce{H_3CCO_2H}\) Write a mechanism for the hydrolysis of methyl 2,4,6-trimethylbenzoate that occurs when the ester is dissolved in concentrated sulfuric acid and the solution poured into a mixture of ice and water (see Section 18-3A): Exercise 18-29 Grignard reagents add to \(\ce{N}\),\(\ce{N}\)-dialkylalkanamides, \(\ce{RCONR'_2}\), to give ketones after hydrolysis.

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