Hydroxamoyl Halides

Substituted hydroxamoyl chlorides were synthesized for the first time by Werner and his students in 1894. In the same year, the parent hydroxamoyl chloride was obtained by Nef. 

The nomenclature of this class of compounds is not at all clear. For example, the following names can be found in the literature hydroxamic acid chlorides, hydroxamic chlorides, hydroximic chlorides (Beilstein lists them as Hydroximsaure chloride ), and acyl and aroylchloride oximes. The latter names are used by Chemical Abstracts, Although the name benzoyl chloride oxime for benzhydroxamoyl chloride is formally correct, it does not reflect the close relationship between hydroxamoyl chlorides and hydroxamic acids, their hydrolysis products. In order to be consistent with the nomenclature used in the earlier chapters, I prefer the term hydroxamoyl to hydroxamic chloride. The interrelationship of the halides with the corresponding acids is shown below, and R is representative of the alkyl, aryl, acyl, aroyl, and carbalkoxy group. 

The standard displacement reactions of the chloro group and the elimination to nitrile oxides have been studied by Werner and his co-workers. Weygand and Bauer in 1927 studied the reaction of hydroxamoyl chlorides with alkali salts of ethyl cyanoacetate they obtained isoxazole derivatives. Likewise, Quilico and his students utilized hydroxamoyl chlorides to synthesize numerous isoxazole derivatives. 

One of the most important reactions of hydroxamoyl chlorides involves dehydrochlorination to nitrile oxides, and the renewed interest in the 1,3-cycloaddition reactions has focused attention again on the nitrile oxide precursors. 

In view of the ready availability of hydroxamoyl chlorides, and their numerous possibilities for transformations, they will most certainly become more important in the years to come. 

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Carbonimidoyl dihalides Imidoyl halides Haloformamidines Haloformimidates Halothioformimidates Hydroxamoyl halides Hydrazidoyl halides... 

Other substituents, such as the pseudohalo groups (CN, NCO, OCN, NCS, SCN) and carboxyl groups, can be attached to the --C(X)=N— system, and compounds of this type are discussed within the outlined scheme. Likewise, O-substituted derivatives of hydroxamoyl halides are included in Chapter 6. Since the imidoyl halides can be part of a heterocyclic system, the cyclic homologs are treated separately in the last chapter. The fully aromatic compounds, such as halopyridines, halopyrimidines, and halo-1,3,5-triazines, are discussed only briefly in Chapter 8, as their chemistry is somewhat different. 

The hitherto-obtained hydroxamoyl halides are listed in Tables I-III. 

Hydroxamoyl halides are colorless-to-yellow solid compounds, which sometimes melt with decomposition because of elimination of hydrogen halide. Exceptions are some of the lower aliphatic derivatives, which are distillable liquids. 

The nomenclature of the imidoyl halides is not clearly established I have therefore attempted to select names which identify the compounds as imidoyl halides, and which furthermore, relate to their chemistry. For example. Chemical Abstracts lists the hydroxamoyl chlorides as oximes of the corresponding carboxylic acid chlorides. Although this name is formally correct, it does not reflect the chemistry of this class of compounds, which is closely related to hydroxamic acids, its hydrolysis products. 

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