Syntin

Syntin is a hydrocarbon with the molecular formula C₁₀H₁₆ used as a rocket fuel. It is a mixture of four stereoisomers (see below). It has a density of 0.851 g/mL and a boiling point of 158 °C. Due to the presence of three strained cyclopropane rings, the molecule has a highly positive enthalpy of formation: Δ_fH°(l) = 133 kJ/mol (980 kJ/kg, the average value for the isomeric mixture), bringing additional energy into the combustion process. It has advantages over the traditional hydrocarbon fuels, such as RP-1, due to higher density, lower viscosity, and higher specific heat of oxidation.

Syntin was used in the Soviet Union and later Russia as fuel for the Soyuz-U2 rocket from 1982 until 1995.

It was first synthesized in the USSR in 1959 and brought to mass production in the 1970s. It was prepared in a multi-step synthetic process from easily obtained acetylcyclopropane (the 3rd molecule):

After dissolution of the USSR, the production of this fuel was halted due to the expense of the synthesis. On September 3, 1995, Soyuz TM-22, the seventy-first and last Soyuz-U2 rocket launched, being the last rocket fueled with Syntin.