Phosgene substitute phosphorus chloride

Phosphorus chlorides have usually been used, but phosgene and thionyl chloride are also effective . Generally, heating l-alkyl-2-pyridones with phosphorus chlorides has led to the isolation of 2-chloropyridines, but in some cases the intermediate l-alkyl-2-chloropyridinium salt has been isolated (p. 223). l-Methyl-4-pyridone also produced 4-chloro-l-methylpyri-dinium chloride which gave 4-chloropyridine and methyl chloride when heated Other examples of the conversion of 1-substituted 4-pyridones into 4-chloropyridinium quaternary salts are known 7 Examples of that of l-aryl-2-pyridones into 2-chloropyridines are rarer but exist 25 ... 

Guanidines have been prepared by the reaction between an amine, or an amine salt, and a host of other reagents, such as a thiourea in the presence of lead or mercuric oxide [83, 157, 158], carbodi-imides [140, 174, 175],calcium cyanamide [176, 177], isonitrile dichlorides [178—180], chloroformamidines [181], dialkyl imidocarbonates [182], orthocarbonate esters [183], trichloro-methanesulphenyl chloride [184], and nitro- or nitroso-guanidines [185-188]. Substituted ureas can furnish guanidines, either by treatment with amines and phosphorus oxychloride [189], or by reaction with phenylisocyanate [190] or phosgene [191]. 

Substituted phenyl salicylates can be prepared by heating salicylic acid and the appropriate phenol in the presence of phosphorus oxychloride,34 5 phosphorus trichloride,4 5 phosphorus pentachloride,4 6 phosgene,4 or thionyl chloride,4 or by heating the phenol and salol.7... 

These compounds and their reactions will be dealt with in Section II, E, but it may be mentioned here that treatment of 1,2-benziso-thiazolinone (25) with phosphorus pentachloride,17 phosphoryl chloride,18,19 phosgene, or oxalyl chloride20,21 affords 3-chloro-l,2-benzisothiazole (26). If the 1,2-benzisothiazoline is substituted at the nitrogen atom, then a salt similar to 21 is the product. 

There are two general routes to arylsulfonyl chlorides. The first involves the conversion of an already sulfur-substituted aromatic compound to the sulfonyl chloride. Thus arylsulfonic acids or their alkali metal salts yield sulfonyl chlorides by treatment with a variety of chlorinating agents such as phosphorus pentachloride, thionyl chloride, phosgene, and chlorosulfonic acid. Alternatively, substituted thiophenols or aryl disulfides can be oxidized by chlorine-water to the sulfonyl chloride.6... 

The ethylidene, or unsymmetrical di-halogen substitution products of ethane, are not of much importance, because they do not easily undergo reaction. They are prepared by the reactions just described, viz., from aldehyde by the action of phosphorus penta-chloride, -bromide, or -iodide. Also by the action of phosphorus chlor-bromide, PCl3Br2, or of carbonyl chloride (phosgene), COCI2. They may also be made by the further halogenation of the mono-halogen ethanes ... 

The reaction of V-cyanocarboximidamide with (chloromethylene)iniinium salts provides another important route to substituted 1,3,5-triazines.394,395 The (chloromethylene)iminium salts are prepared in situ from the corresponding amides, thioamides or dithiocarbamates and phosphoryl chloride, phosphorus pentachloride or phosgene (cf. Houben-Weyl, Vol. E5,... 

The reagent is used as a mild substitute for phosgene, thionyl chloride, or phosphorus pentachloride. The by-products resulting from the reactions involving ox-alyl chloride are usually gases (HCI, CO, and CO2). 

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