The physical and optical properties of carbodiimides [thesis]

Philip Harvey Mogul
= |\|d. Isocyanate f. Carbodiimide dialkenecarbodiimides with an unbranched chain (diallyl-and allyl-carbodiimides) are stable as monomers only when a polymerization inhibitor has been added (4). The aromatic carbodiimides differ considerably in their stability (8). For example, N,N'-di-p-iodophenylcarbodiimide polymerizes very rapidly while the parent compound, N,N'diphenylcarbodiimide, a mobile liquid when freshly distilled, becomes a solid paste upon standing for several days (8). The
more » ... ays (8). The longest period of stability thus far observed for a carbodiimide was for the N,N'-di-p-dimethylaminopheny1 compound which appeared to remain unchanged for over three years (8). The decomposition and polymerization products of carbodiimides are basic, but their composition and structure have not been sufficiently studied. However, it was obser ved that N,N*-diphenyl and N,N*-di-o-tolycarbodiimide polymerization products exist in dimeric and trimeric form (8) These polymers are illustrated in Figure 2. The chemical properties of carbodiimides are primarily determined by their unsaturation, and therefore by their tendency to enter into addition reactions. This (reactivity) refers in particular to reactions with compounds having an active hydrogen atom. a. Reactions with weak acids. Carbodiimides react with hydrogen sulfide to form symmetrical-dialkyl 4 ArN c = NAr ArN=c NAr NAr II c. ArN NAr ArN=C c=NAr Figure 2. Polymers of ^romatic carbodiimides (aryl)-thioureas (2) .RN = C = NR + HSH-^ RNHCSNHR. b. Reactions with phenols. When carbodiimides are heated with phenols, crystalline ethers of pseudoureas are formed (9). RN = C = NR + ArOa-* RNHC(=NR)OAr. c. Reactions with carboxylic acids. Carbodiimides react with carboxylic acids to form acyl ureas or acid anhydrides, depending on the reaction conditions (10). RNHCONHR + (R^WgO RN = C -NR + R*COOH'^ R ' CONRCONHR Dicarboxylic acids react analogously with carbodiimides (11). In fact, the reaction of oxalic acid with carbodiimides is used for the identification and quantitative determination of these compounds (12). The chemical properties of the carbodiimides given above demonstrate that carbodiimides are similar to the other classes of compounds with cumulative double bond systems, in particular to those of the isocyanates. However, under ordinary conditions, carbodiimides react less vigorously than isocyanates with acids, alcohols, and amines (13). Since a relatively large text would have to be written to explain the varied and numerous processes in which carbodiimides are involved, the following list was constructed to illustrate some of their more important uses: a. The g-lactam ring in penicillinoic acid was first closed to form penicillin by means of carbodiimides (14). b. Carbodiimides are used in the synthesis of nucleotides, poly-nucleotides, and coenzymes (15). c. Carbodiimides inhibit the autocatalytic process caused by the formation of carboxylic compounds in polyurethanes. This catalytic process causes the plastic to age (16). d. Carbodiimides can be used as anti-shrink additives in the treatment of textiles (17). e. Water-soluble carbodiimides alone or in combination with CHgO or (CHgO)g impart to photo graphic gelatin emulsions freedom from fogging during storage, increase the photographic speed, improve storage stability, etc. (18). f. Some carbodiimides are found to be more toxic to malignant than to normal cells (19). g. Carbodiimides, in conjunction with other organic compounds, are used with success as cathode depolarizers (20). There has been considerable speculation in the literature concerning structure models for carbodiimides. 7 In 1929, Vorlander (21) suggested a linear model from purely theoretical considerations. Three years later, Bergraann and Schutz (22), utilizing the proposal of Vorlander, attributed the rather large dipole moments they observed for N,N'diphenyl and 4,4'-dimethyl-diphenylcarbodiimide, which were 1.89 and 1.96 D respectively, to a large finite group moment in the NCN molecular fragment. Schneider (23), on the other hand favored an asymmetric structure based upon a linear NCN chain with substituent groups oriented in planes different from each other. In Schneider*s model which is illustrated in Figure 3, the NCN chain is assumed to be located along the Y axis. The bond to one substituent group, Rg, is assumed to lie in the (-Y, -Z) plane, whereas the bond to the other substituent group, lies in the (-X, +Y) plane. When Schneider investigated p,p*-dichlorophenylcarbodiimide, he found that this compound possessed a zero moment. Schneider explained this dipole moment value by equating the aromatic carbon-nitrogen bond moment to the aromatic carbon-chlorine moment, which he assumed were acting in opposite directions. He calculated an independent value for the carbon-nitrogen moment from the observed moment for N,N'-diphenylcarbodiimide and his proposed structure. For an assumed C-N=C bond angle of 121 degrees, Schneider obtained an aromatic carbonnitrogen bond moment of 1.17 D which exactly equaled the aromatic carbon-chlorine bond moment for chlorobenzene. On
doi:10.31274/rtd-180813-3411 fatcat:zoz3bvwo55dp5d6ty47nu3mlba