Reactions with Aromatic Acid Chlorides

Aromatic acid chlorides react with phosphine at 50 °C in absolute pyridine to form mono-, di- and triacylphosphines. For example, PH3 and benzoyl chloride give tribenzoylphosphine, a yellow crystalline compound which is resistent to water and dilute acids but is hydrolysed to PH3 and alkali benzoate by alkalis 

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Further investigation of model reactions revealed that the reaction of aromatic acid chlorides with diols such as butanediol or ethylene glycol was too slow to be useful for kinetically controlled p.vcMdo-high-dilution reactions carried out... 

The reaction of the phospholen (65) with aromatic acid chlorides in the presence of triethylamine, followed by addition of DaO, gives a ready route to aromatic [1-2H]-aldehydes with 100% incorporation of deuterium.55... 

Perhaps the most industrially feasible approach has been developed by Rich and co-workers at General Electric, a palladium-catalyzed silylative decarbonylation reaction of aromatic acid chlorides with disilanes [Eq. (35)].97 One of the silicon centers from the disilane is transferred to the arene whereas the other acts as a chloride acceptor to produce the chlorosi-... 

Biphenyls (64) and dihydro-y-pyrones (63) are formed by the reaction of aromatic acid chlorides with cross-conjugated dienamines51,52 (Scheme 33). 

Aromatic acid chlorides (ArCOCl) are considerably less reactive than the aliphatic acid chlorides. With cold water, for example, acetyl chloride reacts almost explosively, whereas Benzoyl chloride reacts only very slowly. The reaction of aromatic acid chlorides with an alcohol or a phenol is often carried out using the Schotten-Baumaiin technique the acid chloride is added in portions (followed by vigorous shaking) to a mixture of the hydroxy compound and a base, usually aqueous sodium hydroxide or pyridine (an organic base, Sec. 31.11). Although the function of the base is not clear, it seems not only to neutralize the hydrogen chloride that would otherwise be liberated, but also tp catalyze the reaction. 

The corresponding dialkyl zinc reagents have also been used in acylation (equation 103). Under the reaction conditions with aromatic acid chlorides, substituted benzaldehydes are often a by-product. The... 

Aryl cyanates react with aromatic acid chlorides in the presence of anlimony(V) chloride to give 2-aryl-4,6-bis(aryloxy)oxadiazinium salts 5a, b 62 thiocyanates react analogously giving 5c-n but in this case the reaction is of wider scope as both the thiocyanates and the acid chlorides may be aromatic or aliphatic.63,64... 

To protect the secondary amine group (NH) from oxidation 1,4-NpN -bis(butadienyl-2-methyl)-2 3 5 6-tetramethylbenzene was modified by reacting it with aromatic acid chlorides to afford the corresponding 1,4-N,N -bis(butadienyl-2-methyl)-diamido-2p3p5p6-tetramethylbenzene monomers (Scheme 5). The amide pendant group also provides additional steric hinderance surrounding the Ip 3-diene system which would increase the reactivity of the diene in the Diels-Alder reaction by increasing... 

The preparation of amides by reaction of an amine, an acyl chloride, or an acid anhydride in the presence of aqueous alkali is the well-known Schotten-Baumann reaction. Since the rate of reaction of the acyl chloride with amines is greater than the rate of hydrolysis of the acyl chloride, amide formation is favored. In some cases, the stability of acyl chlorides to aqueous caustic solution is surprising. For example, benzoyl chloride may be kept in contact with sodium hydroxide solutions for long periods of time. We presume that a thin layer of sodium benzoate forms rapidly and that this acts as a protective coating unless the benzoyl chloride is stirred or shaken to disturb the protective layer. As a matter of fact, the Schotten-Baumann reaction (and the analogous Hinsberg reaction with aromatic sulfonyl chlorides) appears to be most satisfactory when acyl chlorides are used which are relatively insoluble in water. Many years ago, we noted that the addition of a small percentage of a surfactant (e.g., sodium lauryl sulfate as well as cationic surfactants) assisted in the dispersion of the acyl chloride with an increase in reaction rate. These may have been early examples of phase-transfer reactions. 

Primary aromatic amines differ from primary aliphatic amines in their reaction with nitrous acid. Whereas the latter yield the corresponding alcohols (RNHj — ROH) without formation of intermediate products see Section 111,123, test (i), primary aromatic amines 3neld diazonium salts. Thus aniline gives phcnyldiazonium chloride (sometimes termed benzene-diazonium chloride) CjHbNj- +C1 the exact mode of formation is not known, but a possible route is through the phenjdnitrosoammonium ion tlius ... 

Most aromatic acid chlorides impart a strongly acid reaction when shaken with water (compare Section 111,88). All are completely hydrolysed by boiling with solutions of caustic alkalis and yield no product volatile from the alkaline solution (compare Eaters, Sections 111,106 and IV, 183). They may be distinguished from acids by their facile reactions with alcohols (compare Section 111,27), phenols (compare Section IV,114), and amines (compare Sections 111,123 and IV.lOO). 

As a dibasic acid, malic acid forms the usual salts, esters, amides, and acyl chlorides. Monoesters can be prepared easily by refluxing malic acid, an alcohol, and boron trifluoride as a catalyst (9). With polyhydric alcohols and polycarboxyUc aromatic acids, malic acid yields alkyd polyester resins (10) (see Alcohols, polyhydric Alkyd resins). Complete esterification results from the reaction of the diester of maUc acid with an acid chloride, eg, acetyl or stearoyl chloride (11). 

Tetrahydroharman, m.p. 179-80°, has been prepared by a number of workers by a modification of this reaction, viz., by the interaction of tryptamine (3-)5-aminoethylindole) with acetaldehyde or paraldehyde and Hahn et al. have obtained a series of derivatives of tetrahydronorharman by the use of other aldehydes and a-ketonic acids under biological conditions of pH and temperature, while Asahina and Osada, by the action of aromatic acid chlorides on the same amine, have prepared a series of amides from which the corresponding substituted dihydronorharmans have been made by effecting ring closure with phosphorus pentoxide in xylene solution. 

The electrophile 4 adds to the aromatic ring to give a cationic intermediate 5. Loss of a proton from 5 and concomitant rearomatization completes the substitution step. Subsequent hydrolysis of the iminium species 2 yields the formylated aromatic product 3. Instead of the highly toxic hydrogen cyanide, zinc cyanide can be used. The hydrogen cyanide is then generated in situ upon reaction with the hydrogen chloride. The zinc chloride, which is thereby formed, then acts as Lewis acid catalyst. 

Just as an aromatic ring is alkylated by reaction with an alkyl chloride, it is acylated by reaction with a carboxylic acid chloride, RCOC1, in the presence of AICI3. That is, an acyl group (-COR pronounced a-sil) is substituted onto the aromatic ring. For example, reaction of benzene with acetyl chloride yields the ketone, acetophenone. 

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