The Preparation of Thiocyanoacrylates

In this note we report the preparation of hitherto unknown thiocyanoacrylates. These compounds are conveniently prepared by displacement from their readily synthesized anthracene adducts by treatment with relatively strong dienophiles such as maleic anhydride’ or even, as we have discovered, ethyl cyanoacrylate. Utilization of the latter material in excess provides a very convenient method for the preparation of thiocyanoacrylate-containing ethyl cyanoacrylate solutions with improved moisture-resistant properties when polymerized between metals.

The thiocyanoacrylate-anthracene adducts were prepared in high yield by reacting cyanoacrylyl chloride-anthracene adduct with the appropriate lead mercaptide in dry ether.2 The S-dodecyl thiocyanoacrylate-anthracene adduct was thus obtained as a colorless crystalline solid with melting point 62-64°C (IR v C(S) = 0.1683 s cm-’). Reacting together equimolar quantities of maleic an- hydride, the ,displacing dienophile,’ and the thio anthracene adduct in refluxing xylene for 42 h* gave the near-theoretical yield of maleic anhydride-anthracene adduct, which came out of solution on cooling to room temperature as colorless crystals which were filtered off. The last traces of this material were similarly removed following the addition of a large volume of pentane to give the thiocyanoacrylate as a very pale brown heavy oil after removal of volatiles. Methyl acetylene di- carboxylate was also found to displace the thiocyanoacrylate from its anthracene adduct.

A thiocyanoacrylate-containing ethyl cyanoacrylate solution was obtained by reacting together excess ethyl cyanoacrylate with the thiocyanoacrylate-anthracene adduct in refluxing xylene for 5 h* (SO2 bleed). The high reactivity of the ethyl cyanoacrylate dienophile in the Diels Alder dis- placement would appear to reside in the higher electron withdrawing capacity of C(0) OCHzCH3 over that of C(0)SR. The S-dodecyl thiocyanoacrylate-containing solution (ca. 10% level of additive) possessed significantly improved moisture resistance over ethyl cyanoacrylate with no additive’ after polymerization between grit-blasted mild steel lapshears exposed to humid aging.

TABLE I Tensile Shear Strength Half-Inch Overlap Grit-Blasted Mild Steel Lapshears (kg/cm2; Percent

Retention Tensile Shear Strength)

After 3 After 7 days Composition days (RT) (4OoC/95% RH)

Ethyl CA (with appropriate quantity ethyl cyanoacrylate- 194 100 (48)

Ethyl CA + 8% S-dodecyl thiocyanoacrylate 93 86 (85) anthracene adduct)

As can be seen in Table I, utilization of S-dodecyl thiocyanoacrylate in the ethyl CA renders a bond of comparatively low tensile shear strength exhibiting considerably improved moisture resis- tance.

* The displacement was readily monitored by recording the NMR spectra of regularly withdrawn aliquots. The appearance of new resonances corresponding to vinyl protons of thiocyanoacrylate a t 6.83 and 6.34 ppm (a), (dodecyl derivative) were indicative of the motion observed. Vinyl protons of ethyl cyanoacrylate appear a t 7.03 and 6.60 ppm (a), respectively.

+ To this ethyl cyanoacrylate sample was added an appropriate quantity of ethyl cyanoacrylate- anthracene adduct to “blank out” the effect of this coreaction product of displacement.

Journal of Polymer Science: Polymer Chemistry Edition, Vol. 19,2655-2656 (1981) 0 1981 John Wiley & Sons, Inc. CCC 0360-6376/81/102655-02$01.00

2656 NOTES

References

1. C. J. Buck, US. Patent 4,013,703,1977. 2. G. Braude, J. Org. Chern., 22,1675 (1957).

S. HARRIS

Research & Development Loctite Ltd. Dublin, Ireland

Received March 4,1981 Accepted May 15,1981