Acid chlorides anhydrides from

Potassium nitrate may be used for the preparation of acid anhydrides from acid chlorides, by distilling the latter after mixing with the alkaline nitrate.43... 

When we made acid anhydrides from acid chlorides plus car- ase pKaH Jl... 

When we made acid anhydrides from acid chlorides plus car-boxylate salts, we used an anionic nucleophile RCO2 but, when we made amides from acid chlorides plus amines, we used a neutral nucleophile NH3, and not NH2. For proper comparisons, we should include in our table ROH (pXaH = -5 in other words, -5 is the pXa of ROH2) and NH3 (pXgH = 9 in other words, 9 is the pKaofNHj). 

Formation of acid anhydrides from acid chlorides and alkali salts of carboxylic acids is carried out by mixing the reactants and distilling off the anhydride formed. 

Cellulose esters are commonly derived from natural cellulose by reaction with organic acids, anhydrides, or acid chlorides. Cellulose esters of almost any organic acid can be prepared, but because of practical limitations esters of acids containing more than four carbon atoms have not achieved commercial significance. 

Cellulose chloroacetates (30) and aminoacetates (30,31), acetate sorbates (32), and acetate maleates (33) have been prepared but are not commercially important. These esters are made from hydrolyzed cellulose acetate with the appropriate anhydride or acid chloride in pyridine. 

Acid anhydride, amides from, 807 eleclrostatic potential map of, 791 esters from, 807 from acid chlorides, 806 from carboxylic acids, 795 1R spectroscopy of, 822-823 naming, 786... 

Acylation reactions. Methoxyacetophenones and methoxypropiophenones can be obtained from acylation of methyl phenyl ether with the corresponding acid anhydrides and acid chlorides at 70 "C over Envirocat EPZG in 35 to 72 % yield. Other important reactions catalysed by this catalyst include acylation of PhNHCOCHi to acetamidoacetophenones and 1,3,5-trirnethylbenzene to 1,3,5- trimethylacetophenone. 

The alkyl group of the salt of the alkylsulphuric acid can also be made available for esterification if the temperature is raised sufficiently. The formation of esters from acid chlorides or anhydrides need only be recalled here. This method also has practical importance. 

One-pot conversions of 2-hydroxy(acylbenzenes) with anhydrides or acid chlorides to produce coumarins [52-54] and flavones [54-58] under mild liquiddiquid or solidtliquid two-phase conditions via a Baker-Venkataraman type reaction (Scheme 6.19) are catalysed by quaternary ammonium salts. 3-Substituted coumarins are produced from salicylaldehyde and malonodinitrile, or substituted acetonitriles, in high yield (>85%) in a one-pot catalysed sequential aldol-type reaction and cycliza-tion in the absence of an added organic solvent [59]. When 2 -hydroxychalcones are reduced under catalytic two-phase conditions with sodium borohydride, 2,4-cis-flavan-4-ols are produced [60] (see Section 11.3). 

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). 

Preparation of acid anhydrides Acid anhydrides are prepared from carboxylic acids by the loss of water. For example, acetic anhydride is prepared industrially by heating acetic acid to 800 °C. Other anhydrides are difficult to prepare directly from the corresponding carboxylic acids. Usually they are prepared from acid chloride and sodium carboxylate salt (see below). 

The formation of esters from acid chlorides and anhydrides according to the following equation has been discussed ... 

Amides generally are formed from acid chlorides, acid azides, acid anhydrides, and esters. It is not practical to prepare them directly from an amine and a carboxylic acid without strong heating or unless the reaction is coupled to a second reaction that activates the acid (see Exercise 15-25). Notice that esters of phenols are more reactive toward amines than esters of alcohols because phenols are stronger acids than alcohols. 

Carboxylic acid derivatives, as well as aldehydes and ketones, together with the corresponding sulfur compounds, have been included in this section. The reactivity of the 1- and 3-positions is such that in syntheses using acetic anhydride it is often impossible to prevent acetylation. Acyl derivatives may be formed from acid chlorides,44,159-161 cyclobutene-dione derivatives,162 or esters.163 Thus, reaction of a substituted in-... 

Friedel-Crafts reactions have found application to form the 1,2-bond of pyrrolizines. Treatment of anhydride 78 with aluminum chloride gave 93% of acid 79, which on heating in the presence of copper gave a 91% yield of 2,3-benzo-1 H-pyrrolizin-1 -one (17).55 Benzopyrrolizinones (81) have been obtained from acid chlorides (80) by a similar route.56,57 Houben-Hoesch cyclization of nitrile 82 gave 2,3-benzo-lf/-pyrrolizin-l-one (17) in a reaction that resembles the formation of 17 from 16a.58... 

Acid chlorides are often used in these syntheses because they are the most electrophilic of all acid derivatives and because they can be made from the acids themselves with PCI5 or SOCI2. The other important acid derivatives can all be made from acid chlorides or from any compound above them in the chart of reactivity. So you can make amides from acid chlorides, anhydrides or esters but it is very difficult to make any other derivatives from amides. All derivatives except amides can easily be made from the acids themselves. 

In Chapter 12 pyridine was often used as a catalyst in carbonyl substitution reactions. It can act in two ways. In making esters from acid chlorides or anhydrides pyridine can act as a nucleophile as well as a convenient solvent. It is a better nucleophile than the alcohol and this nucleophilic catalysis is discussed in Chapter 12 (p. 282). But nonnucleophilic bases also catalyse these reactions. For example, acetate ion catalyses ester formation from acetic anhydride and alcohols. 

Amides are much more easily prepared from acid chlorides and anhydrides, as discussed in Sections 22.8 and 22.9. 

---