April 22, 2013
Here’s a greener process for making fragrance components. Y.-C. Lee and co-inventors improved the process for making aldehydes that are used as fragrances in soaps, detergents, and cosmetics. Compounds specifically covered are floralozone (1) and lysmeral (2).
Current processes for preparing the compounds require a high-pressure hydrogenation step that the inventors believe is unsuitable for industrial use. The new process begins with the preparation of a phase-transfer catalyst (PTC) that is used to make the desired aldehydes.
The first sequence in the figure shows the synthesis of PTC compounds 5a and 5b by the reaction of alkylbenzene 3a or 3b with HCHO and HBr in HOAc. Intermediate 4a is isolated in 86.9% yield after vacuum distillation; it is then treated with NMe3 to produce PTC compound 5a. The PTC is isolated as a solid, but its yield and purity are not reported.
PTC compound 5b is similarly prepared by way of 4b, isolated in 86.3% yield. The PTCs are used to prepare aldehydes 1 and 2.
In the synthesis of 1, shown the second sequence, compound 4a reacts with isobutyraldehyde in a two-phase mixture of water and toluene that contains PTC 5a. Compound 1 is isolated in 82.8% yield with 95.8% purity by GC. A comparative preparation of 1 that uses n-Bu4NI as the catalyst yields only 54.1% product.
The same procedure, shown in the third sequence, is used to produce lysmeral. Bromide 6 and propionaldehyde react in the presence of PTC 5b to produce 2 in 82.6% yield and 97.3% purity (GC).
The process uses inexpensive reagents. In contrast to earlier processes, it does not require high pressures or produce hazardous wastes. (UFC Corp. [Taipei]. US Patent 8,362,303, January 29, 2013; Keith Turner)