SYNOPSISAlkyl 2-cyano-2,4-pentadienoates and alkyl 2-cyano-2,4-hexadienoates were synthesized and characterized by spectroscopic methods. These were then evaluated as cross-linkers in 2-cyanoacrylate adhesive compositions to improve the heat stability of their adhesive bonds between various metal surfaces. 0 1993 John Wiley & Sons, Inc. I N T R O D U C T I O N3-Substituted-2-cyanoacrylates have been used from time to time either as cross-linkers for alkyl 2-cyanoacrylates or on their own as adhesives apart from other acrylic monomers. These esters are recommended to use in the alkyl2-cyanoacrylate adhesive compositions, aiming at improvement of the joint bond strength under higher-temperature conditions.'-6 Most of the literature available on their synthesis and their compounding with alkyl 2-cyanoacrylates is in the form of patents that are often misleading. In the present communication, the synthesis of 3-substituted-2-cyanoacrylates such as alkyl2-cyano-2,4-pentadienoates, and hexadienoates and their effect in alkyl 2-cyanoacrylate adhesive composition on heat aging of adhesive bond strength has been discussed. EXPERIMENTAL Synthesis of AlkylDifferent alkyl 2-cyano-2,4-pentadienoates were prepared by reacting corresponding cyanoacetate with acrolein in the presence of a zinc chloride catalyst: Zinc chloride (0.037 mol) and dioxane (40 mL) were taken in a two-neck round-bottom flask, and this mixture was stirred for about 30 min while heating at 70°C using an oil bath. Then, this mixture was cooled to room temperature (25°C). Alkyl cyanoacetate (0.06 mol) and acrolein (0.075 mol) were added slowly to this mixture. The reaction mixture was stirred for 3 h at 25°C. The product was isolated by taking the product in 50 mL of hexane and further extracting with cold dilute hydrochloric acid in ( 3 X 100 mL) portions. the organic layer was separated and dried and the solvent removed under reduced pressure. The crude product was recrystallized from a petroleum ether-ethyl ether (1 : 1) mixture. Attempts to check the purity by the GLC technique have failed due to the polymerization of these compounds over the column at 180°C. The purity of the compounds was therefore checked by spectroscopic methods. Synthesis of Alkyl 2-Cyano-2,4-hexadienoatesAlkyl 2-cyano-2,4-hexadienoates were prepared by reacting crotanaldehyde (0.15 mol) with the corresponding cyanoacetate (0.12 mol) in the presence of a zinc chloride catalyst (0.074 mol) in dioxane (80 mL ) as the solvent medium: 1387

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