Sigma seems to have two products listed for sale as "Cinnamic Aldehyde". One compound clearly seems the trans isomer but the other one seems like an unspecified mixture. (They even have two different CAS nos.: 14371-10-9 vs 104-55-2 )

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What surprises me is that the corresponding SDS lists the Flash Point of one as 71°C and the other as 125°C.

Is this really possible or is this just an error? The boiling points listed seem fairly close: 250°C vs 248°C.

P.S. Even if one accounts for methodological differences in Flash Point Determination e.g. closed cup vs open cup those are typically at worst 10°C apart. Here the flash points seem a good 55°C apart.

What gives?

  • $\begingroup$ Which has the lower flash point? Trans is more stable. Runaway isomerisation of the cis component? Also the cis isomer is rather unstable in air, anway. $\endgroup$
    – Karl
    Jun 27, 2017 at 16:45
  • $\begingroup$ First glance suggests that the first compound is not cis-, but some kind of mixture of isomers. $\endgroup$
    – Zhe
    Jun 27, 2017 at 19:19

1 Answer 1


It is not totally surprising giving that they are stereoisomers. Think about maleic and fumaric acid, which due to their very different properties were given different names. Moreover, but perhaps you are aware of, there is not in general a relationship between boiling point and flash point. In the first case factors which depends on the actual configuration - as molecular symmetry, polarity - should be considered for how they affect intermolecular forces. For the flash point, their influence to the intrinsic stability of the molecule and to the overall shape and accessibility for oxygen, should be considered instead.

For the less experienced ones: in few words volatility is required to reach the concentration (in air) at which the vapour can be ignite at a given temperature (flash point). More a liquid is volatile, easily that concentration is reached. But this does not imply a lower flash point, which depends on the thermodynamics and the kinetics of the reaction between the vapour molecules and oxygen in air.


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