Acyl halides Thionyl chloride

Introduction. Of all acyl halides, the chlorides are the most commonly used. They are usually prepared by the action of phosphorus trichloride, phosphorus pentachloride, or thionyl chloride on the... 

The liquid phosphorus oxychloride, b.p. 107°, is a by-product and is removed by fractional distillation under normal pressure. Unless the b.p. of the acid chloride differs very considerably (say, <] 100°) from that of the phosphorus oxychloride, the acyl halide is liable to contain traces of the latter. In such circumstances it is preferable to use thionyl chloride for the preparation of the acid chloride. 

In the first step, 2-chloro-4-aminobenzoyl chloride hydrochloride is prepared by refluxing a mixture of 25 cc of purified thionyl chloride and 10 g of 2-chloro-4-aminobenzoic acid until all of the solid has gone into solution. To the cooled solution is added 150 cc of dry ethyl ether. A brisk stream of dry hydrogen chloride is passed into the solution until the precipitation of 2-chloro-4-aminobenzoyl chloride hydrochloride is complete. The acyl halide is removed by filtration and dried in a vacuum desiccator. 

Acyl halides, or Non-metal halides MRH Thionyl chloride 1.63/60... 

The formation of an acyl halide involves the reaction of a carboxylic acid with a halogen source. The common halogen sources tire compounds like PX3, PXj, ClOCCOCl (oxalyl chloride), or SO.V2> where. Y is a halogen. The most commonly used acyl halides are the chlorides, and the simplistic reaction is RCOOH —> RCOCl. Figure 12-15 illustrates the mechanism using thionyl... 

Salicylic acid can be converted to salicyloyl chloride [1441-87-8] by reaction with thionyl chloride in boiling benzene. The formation of acyl halide may also extend to reaction with the phenolic hydroxyl. The reaction with phosphoms tri- and pentachlorides is not restricted to the formation of the acid chloride. Further interaction of the phosphoms halide and the phenolic hydroxyl results in the formation of the phosphoric or phosphorous esters. 

The hydroxymethyl compound 43 with acyl halides gave esters of the type 48.166 The acid 49 has reacted via the acyl chloride to give a number of amides of the type 50.154,156 Thionyl chloride converts 43... 

Difficult N-acylations, such as those of A-alkylanilines or a-alkylamino acid derivatives, are most conveniently performed with acyl halides in non-nucleophilic solvents (e.g. DCM, DCP) in the presence of pyridine or DIPEA [13]. Acyl halides can be prepared on insoluble supports under conditions similar to those used in solution. Typical reagents for the preparation of acyl chlorides include oxalyl chloride [19-21], thionyl chloride [22,23], and triphosgene [13]. Anhydrous solvents must be used for all wash-... 

Dimethyl sulfoxide decomposes violently when in contact with a wide range of acyl halides and related compounds, such as cyanuric, acetyl, benzoyl, benzenesulfonyl, thionyl, and phosphoryl chlorides and PC13- DMS should be used with caution as a solvent in exploratory reactions... 

Acyl halides are invaluable acylating reagents and their preparation is therefore of great importance. The conversion of an aliphatic carboxylic acid into the corresponding acyl chloride is usually achieved by heating the acid with thionyl chloride. 

Carboxylic acids react with phosphorous trichloride (PC13), phosphorous pentachloride (PC15), thionyl chloride (SOCl2), and phosphorous tribromide (PBr3) to form acyl halides. 

Thionyl chloride can be viewed as the di(acid chloride) of sulfurous acid. It is even more reactive than the acyl halide. Its reactivity, along with the formation of gaseous products (S02 and HC1), serves to drive the equilibrium to the acyl chloride. The mechanism for this reaction is shown in Figure 19.2. It is interesting to note that thionyl chlo-... 

The conversion of a carboxylic acid to its halide is usually accomplished by thionyl chloride or phosphorus halides. Phosphorus trichloride and glacial acetic acid give acetyl chloride (67%). The other product is phosphorus acid. Phosphorus pentachloride is converted to phosphorus oxychloride (b.p. 103°), from which the acyl halide is sometimes separated with difficulty. This reagent, however, finds use in the preparation of certain higher-molecular-weight halides. .. Most acyl bromides are made from phosphorus tribromide. ... 

Olefinic acyl halides are made from the corresponding acids by treatment with thionyl chloride or phosphorus pentachloride. ... 

Alkoxy and pl)enoxy acyl halides in which the ether group is on an aromatic nucleus or an aliphatic chain are made with thionyl chloride. 

Carboalkoxy acyl halides are made from mono esters of dibasic acids and thionyl chloride or phosphorus pentachloride. Examples are numerous. Halides with the ester group in the beta position are unstable to prolonged heating. Alkyl halide is eliminated with the formation of an anhydride. Under certain conditions a rearrangement occurs in the preparation of ester acid chlorides. The product obtained is a mixture of the expected compound and its isomer in which the ester and acid chloride groups are interchanged, viz., ROjCCHR (CI ) CO,H — RO,C(CH,) CHR COQ. The cyclic anhydride is a likely intermediate. ... 

Acyl halides may be prepared from carboxylic acids by treatment with phosphorus pentachloride or, better, thionyl chloride (Scheme 3.63) the latter gives gaseous by-products. Oxalyl chloride may be used in the same way and again it gives volatile by-products. 

Aromatic carboxylic acids show many properties that parallel those of aliphatic carboxylic acids. Thus acyl chlorides are formed on treatment with thionyl chloride and esters are obtained on treatment with the alcohol and an add catalyst. Benzoate and 3,5-dinitrobenzoate esters are used in the characterization of alcohols and are prepared using the reaction of the acyl halide with the alcohol. 

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