Acyl chlorides triphenylphosphine, carbon tetrachloride

Carboxylic acids can be converted to acyl chlorides and bromides by a combination of triphenylphosphine and a halogen source. Triphenylphosphine and carbon tetrachloride convert acids to the corresponding acyl chloride.100 Similarly, carboxylic acids react with the triphenyl phosphine-bromine adduct to give acyl bromides.101 Triphenviphosphine-iV-hromosuccinimide also generates acyl bromide in situ.102 All these reactions involve acyloxyphosphonium ions and are mechanistically analogous to the alcohol-to-halide conversions that are discussed in Section 3.1.2. 

Acyloxy and phosphorane groups interact when the compound is heated in an inert solvent, and a chromone (not a flavone as stated in the paper) is formed [3827]. 0-Acylsalicylic acids are cyclized to flavones in a similar type of reaction involving carbon tetrachloride and triphenylphosphine [3827]. Higher yields may be obtained by treating a phenolic phosphorane first with an acyl chloride and then with methoxide [3193a]. 

Carboxylic acids can be converted to the corresponding acyl chlorides, which react with an amine containing chromophore. A few methods have been developed for conversion of acids to acyl chlorides. Hoffman and Liao [107] used a mixture of triphenylphosphine and carbon tetrachloride or polystyryldiphenylphosphine to prepare acyl chlorides of fatty acids. The reaction was carried out at 80 °C for 5 min. The intermediate acyl chlorides were then converted to amides with p-nitroaniline or p-melhoxyaniline. Thionyl chloride [108] and oxalyl chloride [109] were also applied to prepare acyl chloride. The conversion with oxalyl chloride was quantitative in 30 min at 70 °C. The commonly used amines were 1-naphthylamine [109] and p-chloroaniline [110]. The final derivatives were separated by RP-HPLC with either gradient [108] or isocratic elution [109,110]. 

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