Acid chloride, alcohols from carboxylic acids

Lithium tetrahydridoaluminate/aluminum chloride Alcohols from carboxylic acid esters... 

Acid chloride, alcohols from, 804 alcoholysis of, 802-803 amides from, 803-804 amines from, 933-935 amjnolysis of, 803-804 carboxylic acids from, 802 electrostatic potential map of, 791... 

Prim, alcohols from carboxylic acid chlorides... 

Alcohols from carboxylic acids, carboxylic acid anhydrides, -chlorides, -esters, and oxo compounds... 

Sodium tetrahydridoborate I zirconium tetrachloride Alcohols from carboxylic acid chlorides s. 44, 33... 

Esters are usually prepared from carboxylic acids by the methods already discussed. Thus, carboxylic acids are converted directly into esters by SK2 reaction of a carboxyfate ion with a primary alkyl halide or by Fischer esterification of a carboxylic acid with an alcohol in the presence of a mineral acid catalyst. In addition, acid chlorides are converted into esters by treatment with an alcohol in the presence of base (Section 21.4). 

Condensation, in which two molecules combine to form a larger molecule and a small molecule, such as Hp or HCl, is eliminated. Such reactions take place when esters are formed from alcohols and carboxylic acids (or acid chlorides). 

Esters are produced by acid-catalysed reaction of carboxylic acids with alcohols, known as Fischer esterification. They are also obtained from acid chlorides, acid anhydrides and other esters. The preparation of esters from other esters in the presence of an acid or a base catalyst is called transesterification. All these conversions involve nucleophilic acyl suhstitu-tions (see Section 5.5.5). 

You remember, of course, that esters can be made from carboxylic acids and alcohols under acid catalysis, so you might expect them to use this type of method. On a small scale, it s usually better to convert the acid to an acyl chloride before coupling with an alcohol, using pyridine (or DMAP + Et3N) as a base this type of reaction might have been a reasonable choice too. 

Direct ester formation from carboxylic acids (R C02H) and alcohols (R OH) works in acid solution but not in basic solution. Why not By contrast, ester formation from alcohols (R OH) and acid anhydrides [(R CO)20)] or chlorides (R COCI) is commonly carried out in basic solution in the presence of bases such as pyridine. Why does this work ... 

The Yamaguchi esterification utilises 2,4,6-trichlorobenzoyl chloride, also known as the Yamaguchi reagent, to form esters from carboxylic acids and alcohols. 

It can be formed from carboxylic acid either by heating it directly with alcohol in presence of a little mineral acid, or via the acid or acyl chloride pathway. In both reactions, the same bond of the carboxylic acid is broken. 

One of the most useful applications of the alkoxy reagents is in the preparation of aldehydes from carboxylic acids by partial reduction of the acid chlorides or dialkylamides. Acid chlorides are readily reduced with lithium aluminium hydride or with sodium borohydride to the corresponding alcohols, but with one equivalent of lithium tri-t-butoxyaluminium hydride, high yields of the aldehyde can be obtained, even in the presence of other functional groups (7.74). 

The mechanism is similar to that for the formation of chlorides from alcohols and thionyl chloride. The hydroxyl group is converted to a good leaving group by thionyl chloride, followed by a nucleophilic acyl substitution in which chloride is the nucleophile (compare with Sec. 7.10). Phosphorus pentachloride and other reagents can also be used to prepare acyl chlorides from carboxylic acids. 

Loss of ethanol from 33 gives oxocarbenium ion 34, and loss of the acidic proton from that species gives butanoic acid (7). The two products of the acid hydrolysis are the carboxylic acid (butanoic acid) and the alcohol (ethanol). As with the hydrolysis of acid chlorides and acid anhydrides before, this mechanism is a series of acid-base reactions. 

Esters are prepared from carboxylic acids by the reaction between an acid chloride and an alcohol or between a carboxylic acid and an alcohol under acidic conditions. Both sulfonic acids and sulfonyl chlorides react with alcohols to form sulfonate esters. When butanesulfonyl chloride (177) reacts with propanol, usually in the presence of a base such as triethylamine, propyl butanesulfonate (180) is formed. A wide range of sulfonyl esters can be formed this way from an alcohol and a sulfonic acid. 

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