Some analysts believe that Egypt provided Syria with chemical weapons on the eve of the October 1973 Yom Kippur war. There are reports that Israeli troops captured stockpiles of gas munitions during the conflict but Syria apparently decided not to use them in spite of its eventual defeat.
In 1979, Egypt’s peace treaty with Israel fractured already-weak Arab unity in the region. Syrian-Turkish relations deteriorated due to conflicts over water rights, among other things. Syria’s then-patron the USSR decided to support theocratic Iran, secular Syria’s adversary, in the Iran-Iraq War.
“The combination of increasing political isolation and observed military deficiencies vis-à-vis Israel together provided incentives for Syria to develop a self-sufficient CW capability,” concludes a Syrian country report from the nonprofit Nuclear Threat Initiative.
As to the technology of Syria’s chemical weaponry, it’s likely the Soviet Union added more advanced equipment to the small Egyptian stockpile during the late 1970s and 1980s. Declassified US documents hold that the USSR provided Damascus with training, delivery systems, and chemical agents themselves, according to CRS nonproliferation experts Mary Beth Nikitin, Andrew Feickert, and Paul Kerr.
In 1983, a US estimate stated that Syria could not make chemical weapons on its own. By the middle and late years of the decade, US intelligence had concluded that Damascus was seeking an indigenous production capability for chemical weaponry. It remains unclear whether Syria ever reached that goal.