Background: Esters of fatty acids with alcohols especially polyols (polyhydroxy alcohols)
have found considerable applications as synthetic greases, synthetic lubricants, in cosmetics, food, and
paint industries. Industrial or conventional esterification is carried out by the condensation of carboxylic
acids with alcohols in the presence of an acid catalyst of homogenous nature. The development of
heterogeneous / solid acid catalysts owing to their safe handling, stability, facile recovery and recycling
ability for esterification reactions has been a subject of great scientific interest. However, the reported
methods have been used for the esterification of acids with mono-alcohols. To the best of our knowledge,
there is no report on the use of graphene-based carbocatalysts for the esterification of fatty acids
with polyhydroxy alcohols.
Methods: The desired sulfonated graphene oxide (SGO) was synthesized by following the two step approach
in which first step involves the synthesis of graphene oxide (GO) from oxidation of graphite
followed by sulfonation with sulfanilic acid under diazotization conditions to give SGO. Esterification
of fatty acids with polyhydroxy alcohols was carried out using 5 wt % of SGO as a catalyst in toluene
at 110 °C for 6 h.
Results: A number of experiments were performed to optimize the reaction parameters for esterification
of 2,2-dimethyl-1,3-propanediol (DMPD) with caproic acid (C6 acid) as model example. The optimum
condition for the esterification was found to be 5 wt % SGO, 6 h reaction time, and 110 °C. After
optimizing the reaction parameters, the scope of the reaction was further extended to a variety of
long chain fatty acids. The presence of electron releasing ethyl group in 2-ethylhexanoic acid had poor
effect on the conversion. Conversion and selectivity were determined by GC-MS.
Conclusion: The present paper demonstrates the preparation of SGO from GO and sulfanilic acid
through diazotization route. The synthesized solid acid carbocatalyst was used in the esterification of
fatty acids with polyhydroxy alcohols for bio-lubricant applications, which is an important branch of
green chemistry. Importantly, the carbocatalyst showed excellent recyclability, which suggested high
stability of sulfonic acid groups in SGO.