This is an interetsing question and the answer depends on how you apply the definition of a "vacuum".
A vacuum is a region of space in which there is no matter.
Odor from a chemical is transmitted through space by currents in a media such as air or through Brownian motion. Brownian motion is movement of particles brought about through the property of matter that holds that the particles move in random motion until they encounter an obstacle or force which changes their motion.
So, it is possible for the molecules of a substance to move through a vacuum due to Brownian motion. However, to detect an odor there must be a detection device present (i.e.: the nose). The nose is matter so it would have to be "in the vacuum" to detect the molecules. The presence of the nose in that space no longer allows the space to be a vacuum. Similarly, once the molecules of the chemical begin to move through the space of the vacuum by Brownian motion, the space is no longer a vacuum.
However, in the most simple interpretation of the question, the distance of seperation created by a vacuum can be crossed by molecules of matter as they experience Brownian motion.