Advanced Organic Chemistry/ Organic Synthesis – CH 621 Ultrasound
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Advanced Organic Chemistry/ Organic Synthesis – CH 621 Ultrasound Assisted Organic Synthesis (Sonochemistry) Bela Torok Department of Chemistry University of Massachusetts Boston Boston, MA 1 Ultrasonics/Sonochemistry - Historical Overwiev Ultrasonics - Ultrasounds (20-10 000 kHz) - 1880 Piezoelectricity (Curie brothers) - 1893 Galton - 1912 TITANIC - 1912 Behm (Echo technique) - 1917 Langevin (Ultrasonic variation, Icebergs, Submarines) - 1945 Application in chemistry 2 Ultrasonics/Sonochemistry –Basics Frequency ranges of sound 3 Ultrasonics/Sonochemistry – Basics Sound transmission through a medium 4 Ultrasonics/Sonochemistry – Acoustic Cavitation Bubble size and cavitation dynamics Formation of an acoustic bubble Transient cavitation 5 Ultrasonics/Sonochemistry – Acoustic Cavitation Acoustic cavitation in a homogeneous liquid Suslick - ~ 4-5000 K 6 Ultrasonics/Sonochemistry – Acoustic Cavitation Acoustic cavitation in solid/liquid system 7 Ultrasonics/Sonochemistry – Acoustic Cavitation Acoustic cavitation in solid/liquid system 8 Ultrasonics/Sonochemistry – Acoustic Cavitation Acoustic cavitation in liquid/liquid system 9 Ultrasonics/Sonochemistry – Sonochemical Effect Specific ultrasonic effect ? Yes and No No - another internal heating approach Yes - The temperature dependence of EA of different reactions could be significantly different – change in selectivities - Very effective mixing - Cavitation - Surface cleaning 10 Ultrasonics/Sonochemistry – Experimental Parameters 1. Acoustic frequency Increasing frequency – increasing energy Theory - usually higher reaction rate Real life – optimum frequency as we have to balance reactivity/selectivity The effect is different for every reaction and general rule can not be made. 11 Ultrasonics/Sonochemistry – Sonochemical Effect 2. Acoustic power Similar as frequency, however, the extent of increase is limited Optimum 12 Ultrasonics/Sonochemistry – Sonochemical Effect 3. Temperature Cavitation bubbles – energy of collapse Pressure inside the bubble In general lower temperature is better, but again there is an optimum as higher temperature increases the probability of the cavitation 13 Ultrasonics/Sonochemistry – Sonochemical Effect 4. External (static) pressure Not quite clear, but in general higher pressure is better. Role of particles (ultrafiltration) 14 Ultrasonics/Sonochemistry – Sonochemical Effect 5. Gas Polytrop ratio (γ= Cp/Cv), thermal conductivity, and solubility Usually inert gases are the best (noble gases) 15 Ultrasonics/Sonochemistry – Sonochemical Effect 6. Solvent Should be as inert as possible, and stable toward ultrasounds Sonolysis of the solvent Usually high bioling point is preferred, but it is controversial as diethylether is a good solvent in many applications. 16 Ultrasonics/Sonochemistry – Experimental Parameters Experimental parameter Physical parameter Effect Acoustic frequency Period of bubble collapse Change in the size of the bubbles Acoustic power Size of the reaction zone The number of cavitation phenomena in a unit volume Temperature Vapor pressure of liquid The content of bubbles, the Themal activation intensity of collapse Secondary reactions Static pressure Total pressure Intesity of collapse Solubility of gas The content of bubbles Gas Politrop ratio Intesity of collapse Thermal conductivity Primer and secondary reactions Chemical reactivity The content of bubbles solubility Solvent Vapor pressure Intesity of collapse Surface tension Limit of transient cavitation Viscosity Primer and secondary reactions Chemical reactivity 17 Ultrasonics/Sonochemistry – Transducers Galton whistle (physical) Liquid whistle (physical) Piezoelectric sandwich transcducer Magnetostrictive transcducer 18 Ultrasonics/Sonochemistry – Reactors 19 Ultrasonics/Sonochemistry – Applications - Electronics industry (coating with metals) - Therapy (surgery with ultrasounds), diagnostics - Food industry - Materials (metallurgy) - Synthesis - Environmental applications 20 Ultrasonics/Sonochemistry – Synthesis Applications in Organic Synthesis 1. Homogeneous Sonochemistry - Aqueous medium - Non-aqueous media 2. Heterogeneous Sonochemitsry - Phase Transfer Catalysis - Reactions with metals - Heterogeneous Catalysis 3. Enzyme reactions 21 Ultrasonics/Sonochemistry – Synthesis 1. Homogeneous sonochemistry 1.1. Aqueous sonochemistry COOH HOOC Br2 2 Br (2.8) H + OH H2O H O ))) H + OH 2 COOH COOH H 2 H 2 2 OH H2O2 2 OH O + H2O 2 O O2 0,5 O + 2 H 2 H2O COOH COOH (2.9) ))) OH 22 Ultrasonics/Sonochemistry – Synthesis 1. Homogeneous sonochemistry 1.2. Non-Aqueous sonochemistry 23 Ultrasonics/Sonochemistry – Synthesis 1.2. Non-Aqueous sonochemistry CCl3 R R Cl CCOONa, CH CN 3 3 + R (2.14) + N ))) N I- N CCl3 R' R' R' 70-100 % R R R tBuOK (2.15) + ))) N N OtBu N O I- Me Me Me 85-98 % O CCH3 CH2 R R CH COCH , NaOH 3 3 + R (2.16) ))) + N CH N N I- 2 Me Me C Me O CH3 91 - 98 % 24 Ultrasonics/Sonochemistry – Synthesis 1.2. Non-Aqueous sonochemistry o O 90 C, toluene O P + EtO P H OEt EtO EtO NMe NHMe Yield (%) 15 min 30 min 60 min 120 min stirring 0 0 <5 37 sonication 12 32 67 82 25 Ultrasonics/Sonochemistry – Synthesis 1.2. Non-Aqueous sonochemistry O O O R R' R" O + + R R' R" O O R R' R" Yield (%) stirring 10-53 sonication 57-93 26 Ultrasonics/Sonochemistry – Synthesis 1.2. Non-Aqueous sonochemistry ))) + H OO + O2 OO + OOH + Mo(CO) + 6 OH + OOH O 27 Ultrasonics/Sonochemistry – Synthesis 2. Heterogeneous sonochemistry 2.1. Phase transfer catalysis 28 Ultrasonics/Sonochemistry – Synthesis 2.1. Phase transfer catalysis Cl NaOH + CHCl :CCl 3 2 Cl 0.7-5h 74-99% NaOH + CHCl3 TEBA H CCl2H H CCl2H 4.3 1 stirring9h 15% sonication, 3h 83% 29 Ultrasonics/Sonochemistry – Synthesis 2.1. Phase transfer catalysis 30 Ultrasonics/Sonochemistry – Synthesis 2.2. Reactions with metals R Li R O +R"-Cl R' OH R' ))) R" 10-40 min 68-99% O Li, THF R R +R'-Cl O OLi ))) R' 72-99% 31 Ultrasonics/Sonochemistry – Synthesis 2.2. Reactions with metals COOEt EtOOC K, toluene COOEt O ))), 5min 83% Zn, DMF RF-X + CO2 RF COOH ))) 35-77% Me C8H17 Me C8H17 Me Me Zn, AcOH ))), 10 min O H H 32 Ultrasonics/Sonochemistry – Synthesis 2.3. Heterogeneous catalysis 33 Ultrasonics/Sonochemistry – Synthesis 2.3. Heterogeneous catalysis 34 Ultrasonics/Sonochemistry – Synthesis 2.3. Heterogeneous catalysis 35 Microwaves/Sonochemistry – References - http://www.shiga-med.ac.jp/chemistry/sonochemRes.html - Luche, J. L., Synthetic Organic Sonochemistry, Plenum Press, 2001 - Suslick, K. S., Ultrasound: Its Chemical, Physical, and Biological Effects; VCH, 1988. - Mason, T. J., Sonochemistry: Current Uses and Future Prospect in Chemical and Industrial Processing, RSC, 1999 36.