Quantitative Gas-Solid Reactions with ClCN and BrCN: Synthesis of Cyanamides, Cyanates, Thiocyanates, and Their Derivatives

Abstract

Gas ± solid reaction techniques allow quantitative cyanations with ClCN and BrCN. Three primary and four secondary cyanamides, a cyanimide, four cyanates, and four thiocyanates were all prepared as solids in 100 % yield from solid anilines, benzimidazoles, imides, phenolates, and thiolates, respectively. Intramolecular solidstate reactions of cyanated o-aminophenol and of cyanated hydrazides gave heterocyclic compounds. When comparable reactions were performed in solution the reported product yields were considerably less than 100 % in all cases. The reasons for the success of the environmentally benign solid-state syntheses are discussed in terms of phase rebuilding, phase transformation, and crystal disintegration. Atomic force microscopy (AFM) of selected systems indicates the occurrence of long-range molecular movements which are governed by the crystal packing. This is evident from the obvious correlations between the molecular movements and the known crystal packing data. A new type of geometric surface feature, a rectangular and a rhombic depression which resembles a swimming-pool basin, was found in the cyanation of o-aminophenol and benzohydrazide.

Organic Solid-State Reactions

“…It produces gradually face-specific surface features. These grow continuously and are clearly seen in the initial surface plots, for example, in Figure 2 for the reactions of benzohydrazide + BrCN to give 2-amino-5-phenyl-1,3,4-oxadiazole hydrobromide [35], or in Figure 3 for the reaction of 4-aminobenzoic acid on (1 0 1) with NO 2 gas to give the corresponding diazonium nitrate. When product crystallization becomes thermodynamically necessary due to increased product concentration, the phase transition (stage 2) occurs as a sudden event that often creates much larger and totally different surface features as exemplified in Figures 2 and 3.…”

“…No migration is necessary when no significant geometric change (<4%) occurs upon the chemical reaction (topotaxy), or when sufficiently large crystallographic voids can accommodate the product molecules. However, that must be secured [35]. © 1998 Wiley, Reprinted with permission from Ref.…”

Organic Solid-State Reactions with 100% Yield

“…Also, the hard to get in pure form cyanates (211) have been quantitatively obtained by reacting cyanogen chloride (gas-solid) or cyanogen bromide (solidsolid) with phenolates, washing away the salts and drying [92] (Scheme 26).…”

“…The product salts are then removed by washing of the products with water. Thus, the various heterocyclic thiocyanates 224a-d are easily obtained in pure form by either gas-solid (ClCN) or solid-solid (BrCN) reaction [92] (Scheme 29).…”

“…The solid-state reactions of cyanogen chloride or cyanogen bromide with the primary and secondary amines 236, 243, and 245 require the addition of an inert base such as trimethylamine if quantitative reactions are desired. Solid volatile BrCN may be reacted via the gas phase in the chosen setup that gives quantitative yields of the cyanamides 242, 244, and 246 after removal of the amine salts [92] (Scheme 34). The crystalline substrate 236a-c, 243, or 245a-c (10 mmol) was placed in a 500-mL flask which was evacuated and filled with a 1:1 mixture of ClCN and trimethylamine (11.7 mmol each), or it was placed in an evacuated 250-mL wide-necked flask connected to a 250-mL wide-necked flask with freshly sublimed BrCN (1.17 g, 11.0 mmol).…”