A solution of $(-)-1\text{-chloro-1-phenylethane}$ in toluene racemises slowly in the presence of a small amount of ${\text{SbCl}}_5$, due to the formation of:

${\text{SbCl}}_5$ is a strong Lewis acid. It reacts with the alkyl chloride to abstract the chloride ion:
$$\text{R-Cl}+{\text{SbCl}}_5\to {\text{R}}^{+}+{\text{SbCl}}_6^{-}$$
The resulting carbocation ($\text{Ph}-{\text{CH}}^{+}-{\text{CH}}_3$) is planar. The chloride ion (or a complexed form) can then attack from either side of the planar carbocation with equal probability, leading to the formation of a racemic mixture.