From Carbonimidoyl Dichlorides

The reaction of the ester carbonimidoyl dichloride 27 with primary amines affords the 

N-4-chlorophenylcarbonyl-N -t-butylcarbodiimide is obtained in a similar manner. The reaction of the bis-carbonimidoyl dichloride 29 with t-butyl amine affords the carbonyl dicarbodiimide 30.  

In the reaction of H2NCONM2CI2 with t-butylamine the relatively stable N-t-BuJ4 -carbamoylcarbodiimide 31, mp 69 °C is obtained in 64 % yield.Using aminoadamantan the corresponding carbodiimide, mp 124-126 °C, is obtained in 80 % yield. 

Chloroformamldines are intermediates in the above transformation of carbonimidoyl dichlorides with amines. Often, bases, such as triethylamine are used to affect their dehydrochlorination to give carbodiimides. For example, the substituted chloroformamidines 32 react with triethylamine to give the relatively stable imidoylcarbodiimlde 33 (R = Et, 

Even methanol can be used for the dehydrochlorination of the chloroformamidines, as shown in the reaction of chlorodiazadienes 34 to give N-trichloromethylcarbonyl-N -alkyl-carbodiimides 35.  

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The addncts derived from carbodiimides and nncleophiles also undergo thermal elimination reactions to regenerate the carbodiimide, and they are therefore of limited preparative value. For example, the elimination of hydrogen chloride from carbonimidoyl dichlorides is used in the synthesis of arenesulfonylcarbodiimides (see Section 9.2.2). Of course, isoureas and isothioureas also undergo elimination reactions. When the elimination of isothioureas is conducted in the presence of heavy metal ions, the insoluble metal mercaptides are precipitated to facilitate the in situ generation of the carbodiimides. 

In addition to the two classical methods of synthesis of carbonimidoyl dichlorides, several new methods were developed more recently. Thus, chlorination of imidoyl chlorides, generated from monosubstituted formamides and thionyl chloride, provides a useful new method to produce a great variety of carbonimidoyl dichlorides Likewise,... 

A recent patent describes the formation of carbonimidoyl dichlorides in the reaction of several aliphatic and aromatic isocyanates with phosphorus pentachloride. This reaction can be conducted using phosphorus oxychloride as solvent, or without a solvent however, only from aliphatic isocyanates diisocyanates are good yields of... 

Tetrachloroethane 1,2-bis-carbonimidoyl dichloride To a solution of 116g (1 mole) of tetramethylethylenediamine in 1000 ml of 1,2,4-tri-chlorobenzene chlorine is added and the exothermic reaction is controlled at 70-80°C. After the exothermic reaction ceases the temperature is raised at the rate of 10-15°C/hr and chlorination is continued with ultraviolet irradiation. When the temperature has reached 190-210 C, the chlorination is continued for 5 hr, and excess chlorine is removed in a stream of nitrogen. On cooling and concentration tetrachloroethane 1,2-biscarbonimidoyl dichloride, m.p. 166°C is obtained. The yield can range from 30-71%, depending upon temperature control. 

The reaction of carbonimidoyl dichlorides with excess water results in complete hydrolysis with formation of the corresponding amine and carbon dioxide ( ). This reaction affords isocyanate as an intermediate, as evidenced by the isolation of 1,3-diphenylurea from the reaction mixture, obtained by treating phenylcarbonimidoyl dichloride with water In the reaction of tetrameric cyanogen chloride with water at 20°C 2-amino-4,6-dichloro-l,3,5-triazine (LXXXVI) is obtained, whereas at 100 C total hydrolysis to cyanuric acid (LXXXVII) occurs... 

From ethylene glycol and carbonimidoyl dichlorides the cyclic acetal XCIII is obtained 35,40 which upon heating in the presence of lithium chloride or aluminum chloride isomerizes to the oxazolidinone derivative XCIV. 

Chlorotolylene-2,4-bis(l,3-diethyleneguanidine) To a solution of 7.5 g of ethyleneimine and 17.3 g of triethylamine in 75 ml of toluene a solution of 12.5 g of 5-chlorotolylene-2,4-bis(carbonimidoyl dichloride) is added dropwise and with stirring, controlling the reaction at 15°C. After stirring for 2 hours at room temperature triethylamine hydrochloride is removed by filtration and, after evaporation of the solvent and crystallization from hexane, 5-chlorotolylene-2,4-bis(l,3-diethyleneguanidine), m.p. 84-85°C is obtained in 32% yield. 

Aromatic acid hydrazides, semicarbazides, and thiosemicarbazides react with carbonimidoyl dichlorides with elimination of hydrogen chloride and formation of the corresponding heterocycles Thus, from... 

The reverse of this reaction is feasible in the aliphatic series, i.e. carbonimidoyl dichlorides can be obtained from isocyanates and phosphorus pentachloride, and subsequent reaction of the carbonimidoyl dichloride with a variety of sulfur compounds produces isothiocyanates. 

Perhaps the best method for conversion of carbonimidoyl dichlorides into isocyanates consists of their reaction with one equivalent of sodium methoxide, followed by thermolysis. Thus, Kodama and Sekiba obtained the triazinyl isocyanate CXXXII from tetrameric cyanogen chloride via the intermediate CXXXIII. Since N-heterocyclic isocyanates cannot be synthesized by direct phosgenation, this method may have general applicability. 

The chloroformamidine XLI, which is obtained from the carbonimidoyl dichloride XLII and dimethylamine, yields on high-temperature chlorination the unusual chloroformamidine XLIII ( ). See also Chapter 2. 

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