Acyl Halogen Compounds

The substitution of carboxylic-hydroxyl in the molecules of orgamc acids by halogen atoms or by the CN group, generally confers toxic properties. 

Among the halogen derivatives of acid radicles especial interest attaches to phosgene or carbonyl chloride because of its great toxic properties, and it was used in the war of 1914-18. 

From its structure it will be seen that phosgene may be considered as carbonic acid in which both the hydroxyl groups are substituted by chlorine atoms. 

Analogues of phosgene, such as carbonyl bromide have been studied at various times, 1 but experiments on the chemical and particularly toxicological properties have only been carried out in the last few years.  

Carbonyl bromide, because of its boiling point (64° C.) and its comparative stability to the action of water would be preferred as a war gas to phosgene were it not for its lower stability to light and its lesser toxicity. 

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Finally, among the various acyl halogen compounds, formyl fluoride, oxalyl chloride, oxalyl bromide, etc., are interesting possibilities as war gases. 

Ketenes are oxo compounds with cumulated carbonyl and carbon—carbon double bonds of the general stmcture R R2C—C—O, where and R2 may be any combination of hydrogen, alkyl, aryl, acyl, halogen, and many other functional groups. Ketenes with R = sometimes called aldoketenes,... 

The carbon-halogen bond distances in acyl halides increase in the direction F < Cl < Br < I, and are similar, but slightly larger than, those of the alkyl halides (Table 7). Nuclear quadrupole resonance frequencies of halogen compounds suggest that the charge density on the chlorine atom of an acyl chloride is greater than that on an alkyl chloride (Table 8). 

Reaction XLVm. (a) Action of Alkali Cyanides on Alkyl and Acyl Halides. (Bl., [2], 50, 214.)—This reaction is capable of very wide application, all the simple alkyl halogen compounds, the acyl halides, and the halogen fatty acids come within its scope. The nitriles so formed yield acids by hydrolysis, so it is frequently the first step in the synthesis of an acid—the preparation and hydrolysis of the nitrile are often combined. The preparations of malonic, succinic, tricarballylic and other acids (Preparations 60, 61, 62) illustrate this. The extension of this reaction to acyl halides is important, and should be referred to, as should the interaction of silver cyanide, and alkyl iodides, to give isonitriles. Mercuric and silver cyanides, it may be noted, give with acyl chlorides and bromides better yields of normal acyl nitriles than do the alkali cyanides. 

Except for lactam n-acyl derivatives, compounds such as esters, anhydrides and halogen anhydrides of carboxylic acids, which can activate lactam polymerization, can also be used as activators (promoters). 

Acyl halides R-C(=0)X X = halogen See Organic Halogen Compounds... 

The trimethylsilylated ylides (1), easily generated from trimethyl chlorosilane and ylides, react with aldehydes 2 to form vi-nylsilanes 3 (2,3). The vinylphosphonium silanolates 4 are also formed. Compounds 3 are versatile reagents for further reactions (4). The ylide J (with R1 =H) reacts with aldehydes 2 to give the dienes j). The oxidation of with the adduct 6, from triphenyl-phosphite and ozone, gives access to a generaT synthesis of acyl-silanes (trimethylsilylketones) (2). The silylated ylides react to form phosphonium salts 7 with halogen compounds. The salts 7.can be desilylated by fluorine ions. The disubstituted ylides JO Tormed can be converted in statu nascendi with aldehydes V[ into the tris-substituted olefin J2 (2,3). In the case of R3-I, vinyl... 

C-Alkylation of the sodio derivative is accomplished by a technique similar to the alkylation of malonic ester. Primary halogen compounds, quaternary ammonium salts,and an alkene oxide have been used as alkylating agents. Alkylation by secondary halides has been less successful. Hydrolysis of the substituted esters to acetylated amino acids is described for leucine (64%) and phenylalanine (83%). Hydrolysis with deacylation has been used to prepare histidine (45%) and phenylalanine (67%). Glutamic acid (75%) is obtained from substituted acylaminomalonates prepared by the Michael condensation of methyl acrylate and the acylated amino esters. ... 

The amount of aluminum chloride used varies with the type of reaction. In the preparation of hydrocarbons the amount of aluminum chloride used varies from 0.2 to 0.3 moles for each mole of halogen compound reacted. In using acyl chlorides for the preparation of ketones the amount of aluminum chloride is about mole per mole, while with anhydrides two moles of the salt are used. Technical grades of aluminum chloride give as good results as the chemically pure substance. In many cases the granular lumpy commercial material is to be preferred to the pure colorless powder. The latter is far more hygroscopic and more difficult to handle, particularly when powdered. 

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