▎ 摘　　要

NOVELTY - Composite catalyst system comprises: (a) zeolite-boric acid-metal chloride catalyst; and (b) reducing metal based catalyst, where (a) comprises boric acid:metal chloride:zeolite in the ratio of 1:1.5:5-1:2:6 and (b) comprises 1% palladium or ruthenium in activated charcoal or graphene. USE - The composite catalyst system is useful for one pot process for the synthesis of menthol from citronellal (claimed), where the menthol is useful in food, beverage, pharmaceutical, health and personal care products. ADVANTAGE - The composite catalyst system: provides the recovered catalysts are further calcinated to regenerate their activity for subsequent use in at least next 5 batch processes with same efficiency (claimed); provides the menthol from one pot process which is eco-friendly, efficient and economical process; is prepared easily through wet impregnation method and is recovered from the reaction system though filtration or centrifugation; restores their catalytic activity in multiple runs; and reduces isopulegol to menthol in same reactor and solvent system with very low hydrogen pressure. The process (P2): is cheaper, operated using green catalyst with moderate operating conditions, carried out in a single reactor, provides good percentage of menthyl acetate or menthyl benzoate, converts good percentage of L-menthol through esterification of menthol enantiomers followed by hydrolysis, is equally effective in enantiomers (+)-citronellal, (-)-citronellal or ( plus minus )-citronellal; utilizes the palladium or ruthenium in activated charcoal or graphene that is effective for conversion of isopulegol to menthol at low hydrogen pressure (10 psi); utilizes the palladium or ruthenium catalysts in activated charcoal or graphene is prepared easily through chemical impregnation method; utilizes the reduction reaction that is equally effective with addition of few percentages of protic solvents and alkali or alkaline earth metal hydrides without external hydrogen pressure; is completed in few minutes by using microwave irradiation; provides both steps of menthol semi-synthesis that are carried out in the same reactor and same solvent system; and recovers the solvent and re-used after the reaction. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for: (1) preparation (P1) of the composite catalyst system, comprising (c) synthesis of zeolite based catalysts comprising (v) mixing beta -zeolite or gamma -zeolite or gamma -sodium-zeolite or silver exchanged zeolite and boric acid in the ratio of 5:1-6:1 under constant stirring at room temperature for 1-2 hours to obtain zeolite-BA catalyst, (vi) drying the zeolite-BA catalyst obtained in an oven at 105 degrees C, (vii) impregnating the dried zeolite-BA catalyst obtained with aluminum chloride, aluminum nitrate or tin(II) chloride in the ratio of 2.5:1 or 3.5:1 using non-protonated solvent for 1-2 hours under constant stirring at room temperature, (viii) drying the zeolite-BA-metal chloride catalyst obtained in oven at 105 degrees C and then placing in furnace at 190 degrees C for calcination to obtain the desired beta -zeolite-BA-aluminum chloride, beta -zeolite-BA-aluminum, gamma -zeolite-BA-aluminum chloride or gamma -sodium-zeolite- BA-aluminum chloride, silver-zeolite-BA-aluminum chloride, beta -zeolite-BA-tin(II) chloride, gamma -zeolite-BA-tin(II) chloride, gamma -sodium-zeolite-BA-tin(II) chloride or silver-zeolite-BA-tin(II) chloride catalyst, (d) synthesis of reducing metal based catalyst comprising dissolving 10 mmol of palladium(II) chloride, palladium(II) nitrate, ruthenium(III) chloride or ruthenium(III) nitrosyl nitrate in 1 N hydrochloric acid and maintaining the pH at 7 using aqueous solution of sodium bicarbonate followed by adding equal volume of 0.05 mmol of sodium borohydride and 0.3 mmol of glucose with stirring for 30 minutes to obtain the colloidal solution, mixing activated charcoal or graphene (99%) with colloidal solution obtained and stirring the solution at 50-60 degrees C for 1-2 hours to obtain the reducing metal based catalyst with 1% palladium or 1% ruthenium loading, and drying the catalyst obtained in furnace at 100 degrees C for 3-4 hours; and (2) a one pot process for the synthesis of menthol from citronellal using the composite catalyst system, comprising synthesis of isopulegol from citronellal comprising taking citronellal and organic solvent (1:8) in a sealed reactor, adding the zeolite based catalysts obtained to citronellal in the reactor in the ratio of 1:10-1:12 under stirring at the boiling point of the solvent for 2-3 hours, filtering or centrifuging the solution obtained to obtain 98% isopulegol (isopulegol+iso-isopulegol), synthesis of menthol from isopulegol comprising pressurizing the isopulegol obtained through external hydrogen pressure of 10-15 psi for 1-2 hours with reducing metal based catalyst obtained in ratio of 8:1-10:1 and stirring at the boiling point of the solvent, filtering or centrifuging the solution obtained followed by short column chromatography using dichloromethane to obtain more than 95% of menthol, and optionally, enriching the L-menthol through esterification of menthol enantiomers to menthyl acetate or menthyl benzoate followed by hydrolysis