Chlorobenzoic anhydride

Thus benzoic anhydride and o chlorobenzoic anhydride (m.p. 79°) can bo readily prepared by this method (compare n-Heptoic anhydride, Section 111,91). It is sometimes convenient to use pyridine as the reaction medium. 

In a modification the acid chloride is treated with excess of dry pyridine whereby the addition complex ArCOCl. CgHjN is formed decomposition of the latter with water aflFords the acid anhydride  

This modification is illustrated by the preparation of p-chlorobenzoic anhydride from p-chlorobenzoyl chloride. 

B3 the slow distillation of an aromatic carboxylic acid and acetic anhydride in the presence of a little phosphoric acid  

CgHgCO—O—COCH3 + CgHgCOOH CgHgCO—O—COCgHg + CH3COOH The equilibria are established comparatively slowly, hence slow distillation is essential. 

H3C0—O—COCH3 + CgHjCOOH CjHgCO—0—COCgHj + CH3COOH 

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Place a mixture of 17 -5 g. p-chlorobenzoyl chloride (1) and 50 ml. of dry pyridine (Section 11,47,22) in a loosely-stoppered 250 ml. flask and warm on a steam hath for 5 minutes. Pour the reaction mixture upon 100 g. of crushed ice and 50 ml. of concentrated hydrochloric acid. The anhydride separates out at once. When the ice has melted sufficiently, filter the mixture by suction. Wash the sohd with 15 ml. of methanol and then with 15 ml. of dry benzene. The yield of crude p-chlorobenzoic anhydride is 14 5 g. Recrystalhse from 250 ml. of dry benzene 13 g. of the pure anhydride, m.p. 192-193°, are obtained. 

B. p-Chlorobenzoic anhydride benzoic anhydride, p,p -di-ckloro-). A mixture of 17.5 g. (0.1 mole) of j -chlorobenzoyl chloride (Note 6) and 50 ml. (0.6 mole) of pyridine in a loosely stoppered 200 ml. flask is warmed on the steam bath for 5 min-... 

The catalytic activity of phosphines 8 and 9 were first evaluated in the KR of ferf-butyl phenylcarbinol using the electron-deficient m-chlorobenzoic anhydride as the achiral acylating agent. Interestingly, not only did these two catalyst display... 

In the following we shall focus on heterogeneous acid-base reactions. One of the best known case studies is the reaction of crystalline benzoic acid with ammonia to form 1 1 ammonium salts [19, 20]. Crystalline p-chlorobenzoic anhydride reacts with gaseous ammonia to give the corresponding amide and ammonium salt [22] a similar reaction has been investigated in the case of optically active cyclopropanecarboxylic acid crystals [23]. 

Significantly higher selectivity was reported for the first time in 1996 by Vedejs et al. using either the C2-symmetric phosphines 1-4 [6, 8] (Scheme 12.1) or the bicyclic systems 5 (Scheme 12.2) [7, 8]. For example, selectivity factors in the range 12-15 were observed when phosphine 2a was used in the acylation of aryl alkyl carbinols with 3-chlorobenzoic anhydride (Scheme 12.1). 

The first example of a chiral nucleophilic promoter that is also capable of catalytic turnover was described by Vedejs et al.[8], who showed that acylation of 2a with ACjO in the presence of the C2-symmetric phospholane 6 (2a Ac20 6 = 1 2.5 0.16) gave 4 with ee = 34 % (44 % conversion,, v = 2.7, s = fas/ siow) while racemic 1 -phenyl-2,2-dimethylpropanol was acylated with m-chlorobenzoic anhydride under the same reaction conditions to yield the corresponding ester 7 with ee = 81 % (25 % conversion, 5=12-15). In a continuation of these studies the bicyclic phosphine 8 was prepared and evaluated (Scheme 2) [9]. It was found that 8 is an efficient catalyst for the resolution... 

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