Sumesh Chandra Upadhyay

An alternative method for the regio- and stereoselective bromination of alkenes, alkynes, toluene derivatives and ketones using a bromide/bromate couple

Mixtures of NaBr and NaBrO3 in two different ratios have been used for highly stereoselective bromination of alkenes and alkynes, and regioselective bromine substitution at the α-carbon of ketones and at the benzylic position of toluene derivatives. The reactions were conducted in an aqueous acidic medium under ambient conditions. The solid reagents were prepared from the intermediate obtained in the “cold process” of bromine manufacture and are stable, non-hazardous and inexpensive to prepare. This procedure provides an efficient and practical alternative to conventional procedures using liquid bromine directly or indirectly.

Four-fold concentration of sucrose in sugarcane juice through energy efficient forward osmosis using sea bittern as draw solution

Clarified sugarcane juice (osmotic coefficient, φ, ∼1.01) was efficiently dewatered through the spontaneous process of Forward Osmosis (FO) employing sea bittern as draw solution. Sea bittern is the mother liquor that remains after recovery of common salt from seawater. It is either discarded to sea or evaporated to higher densities in solar salt pans for recovery of other marine chemicals such as bromine, Epsom salt, potash and magnesium chloride. Compared to seawater (φ = 0.905) which has limited potential as draw solution, the φ values of the sea bittern samples were in the range of 1.41 to 3.24, providing thereby a high osmotic drive. A polyamide thin film composite membrane was used in the study. With 1 bar applied pressure, room temperature operation, and 1 : 8 volume ratio of sugar cane juice to bittern (φ = 2.26; concentrations of main constituents (% w/v): Na+ = 2.83, K+ = 2.03, Mg2+ = 7.42, Cl− = 23.48, SO42− = 8.42), sucrose concentration in the juice was enhanced from 10.5% (w/v) to 40.6% (w/v) over 4 h, with average flux of 13 L m−2 h−1. Sucrose loss was <3%. Energy computations indicated a saving of 69 kg of bagasse per m3 of raw juice, assuming all process energy (steam/electricity) is derived from bagasse. Epsom salt of high purity was recovered from the spent draw solution upon chilling.

Clean synthesis of crystalline p-nitrobenzyl bromide from p-nitrotoluene with zero organic discharge

2 : 1 : 3 NaBr-NaBrO3-NaCl (obtainable as a low cost and eco-friendly reagent from an alkaline bromine intermediate) has been utilized previously in a number of bromination reactions. One such reaction is the conversion of p-nitrotoluene (PNT) to p-nitrobenzyl bromide (PNBBr) used widely for functional group protection. In the present work, selective cold (0–5 °C) crystallization of PNBBr from the reaction mixture containing ca. 2.5 M PNBBr along with 2.5–5.0 M PNT in ethylene dichloride (EDC) was found to be a winning move which led to gains in two fronts. It allowed the bromination reaction to be carried out cleanly and also enabled direct recycling of the mother liquor in the subsequent batch. Para NO2-Ph-CHBr2 impurity, which built up gradually in the reaction mixture over 8 batches, was converted into PNBBr/PNT through treatment of the mother liquor with NaBH4, thereby helping to recycle the liquor perpetually and eliminate organic waste. EDC was the sole solvent in the entire process and its losses were minimal. The combined yield of isolated and recoverable PNBBr was 98.30% with respect to PNT consumed. The reagent utilization efficiency was 98.26%.