Carboxylate, reaction with acyl chlorides

Amines are convert ed to amides on reaction with acyl chlorides Other acylating agents such as carboxylic acid anhydrides and esters may also be used but are less reactive... 

The alcohol groups of carbohydrates undergo chemical reactions typical of hydroxyl functions They are converted to esters by reaction with acyl chlorides and carboxylic acid anhydrides... 

Water, alcohols, ammonia, or amines are the nucleophiles that are usually employed in reactions with acyl chlorides. The products of these reactions are carboxylic acids, esters, or carboxamides according to the following reactions. 

After acyl halides, acid anhydrides are the most reactive carboxylic acid derivatives. Although anhydrides can be prepared by reaction of carboxylic acids with acyl chlorides as was shown in Table 19.1, the three most commonly used anhydrides are industrial chemicals and are prepared by specialized methods. Phthalic anhydride and maleic anhydride, for example, are prepared from naphthalene and butane, respectively. 

Thioesters have the general formula RCSR. They resemble their oxygen counterparts RCOR (oxoesters) in structure and reactivity more than other carboxylic acid derivatives such as acyl chlorides, acid anhydrides, and amides. Thioesters can be prepared from thiols by reaction with acyl chlorides or acid anhydrides in much the same way as oxoesters are prepared from alcohols. 

Acyl chlorides are readily available They are prepared from carboxylic acids by reaction with thionyl chloride... 

The reaction of alcohols with acyl chlorides is analogous to their reaction with p toluenesulfonyl chloride described earlier (Section 8 14 and Table 15 2) In those reactions a p toluene sulfonate ester was formed by displacement of chloride from the sulfonyl group by the oxygen of the alcohol Carboxylic esters arise by displacement of chlonde from a carbonyl group by the alcohol oxygen... 

Acylation. A/-Acylation and related reactions ate brought about in straightforward ways with acyl chloride or acid anhydride, although the proximity of the carboxyl group may produce other reactions, eg, oxa2olinone formation, under some conditions. 

The customary method for the laboratory synthesis of acid anhydrides is the reaction of acyl chlorides with carboxylic acids (Table 20.1). 

These reactions are most important for the preparation of acyl fluorides. " Acyl chlorides and anhydrides can be converted to acyl fluorides by treatment with polyhydrogen fluoride-pyridine solution" or with liquid HF at — 10°C. Formyl fluoride, which is a stable compound, was prepared by the latter procedure from the mixed anhydride of formic and acetic acids. Acyl fluorides can also be obtained by reaction of acyl chlorides with KF in acetic acid or with DAST. Carboxylic esters and anhydrides can be converted to acyl halides other than fluorides by the inorganic acid halides mentioned in 10-77, as well as with PhsPXa (X = Cl or but this is seldom done. Halide exchange can be carried out in a... 

A wide range of A-acylbenzotriazoles 915 have been prepared under mild conditions in reactions of carboxylic acids with thionyl chloride in the presence of fourfold excess of benzotriazole, including R = alkyl, a-haloalkyl, a-alkoxyalkyl, alkenyl, alkinyl, aryl, and heteroaryl <2003S2795, 2004RQM275>. They represent convenient acylating agents for variety of nucleophiles. Synthetic applications of such compounds have been reviewed <2005SL1656>. 

The carboxylic functionalities inserted onto the tubes can be used as platforms to obtain further transformations (Fig. 3.5). A commonly utilized route is the reaction of carboxylic groups with thionyl chloride or oxalyl chloride to prepare the corresponding acyl chlorides, which are useful intermediates for amidation or esterification reactions. Amides can also be prepared directly from the acids by means of standard solution chemistry conditions, using carbodiimide derivatives in the presence of the selected amine. 

Less extended investigations have been carried out for the stereochemistry of further substitution reactions, which mostly proceed with lower regioselectivities a-carboxylation (inversion) reaction with methyl chloroformate in the a-position (inversion) a-acylation by 2,2-dimethylpropanoyl chloride (inversion)" y-methylation by methyl iodide (anti-S g) and methyl triflate syn-S f° , intramolecular reactions with allyl chlorides (a, inversion or y, awh -S see Section IV.C.3). 

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