sonochemistry: ultrasound applications in organic ... - The Stoltz Group
sonochemistry: ultrasound applications in organic ... - The Stoltz Group
sonochemistry: ultrasound applications in organic ... - The Stoltz Group
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DEFINING THE LAWS OF SONOCHEMISTRYA specific nature of <strong>sonochemistry</strong> is suggested Ando etal JCSCC, 1984, p439BrKCN/Al 2 O 3CN83% 76%+ regioisomersSTIRREDSONOLYSEDSonication seems to obey some rules of its own• An empirical systemization of <strong>sonochemistry</strong> has been published (Luche, J.L. Advances <strong>in</strong> Sonochemistry, Vol3,1993, p 85 and TL, 1990, 4125)• Effects are both chemical and mechanicalRULE 1Reactions that proceed via radical or radical ion <strong>in</strong>termediates are most likely to be sonochemically <strong>in</strong>fluencedRULE 2In heteregenous systems, reactions proceed<strong>in</strong>g via ionic <strong>in</strong>termediates can be stimulated by mechanical effects.Usually the effect is comparable to efficient mix<strong>in</strong>gRULE 3Heterogenous reactions with mixed mechanisms (radical and ionic). <strong>The</strong>se may be enhanced <strong>in</strong> a convergent way(chemically for the radical and mechanical for the ionic) or a switch may occur where the radical pathway is enhancedand "change" the reaction productsFactors affect<strong>in</strong>g sonochemical reactions: frequency, power, reaction temperature (low temperature can lead tohigher reaction rates!), overpressure, solventSONOCHEMICAL REACTIONS IN ORGANIC SYNTHESISHOMOGENOUS REACTIONS - Have received less attention for sonochemical activationK<strong>in</strong>etic StudiesON 3)))N C OPorter etal. JACS, 1938, 1497Enhanced <strong>in</strong>itial rateHydrolysisO 2 NOOR+H 2 O)))35 o CROOH+O 2 NOHKristol etal. TL, 1981,90714-15% enhancement<strong>in</strong>dependentof R group(CH 3 ) 3 C-ClH 2 O/ Ethanol)))(CH 3 ) 3 C-OH+ HClMason etal. Ultrasonics Int. '85Proc., Butterworth, U.K., 839• Effect of <strong>ultrasound</strong> <strong>in</strong>creased with EtOH content with a maximum effect at 50% w/w• Rates of reaction under sonolysis <strong>in</strong>creased as temp was reduced from 20 o C to 10 o C
Sonolysis of some solvents may occur: H 2 O, CCl 4 , CHCl 3 . We can take advantage of this <strong>in</strong> synthesisSonoisomerizationCO 2 MeR• X•CO 2 Me- X•MeO 2 CElp<strong>in</strong>er etal. Nature, 1965, 945CO 2 Me)))XCO 2 MeCO 2 MeR-XA Variation of the Hunsdiecker Reaction (Dauben etal. JOC, 1989, 6101)NOSROCl 3 C• X•)))10 - 15 m<strong>in</strong>, 33 o CCl 3 C-XNSCCl 3 + CO 2+R•X•R-ClCleavage of the T<strong>in</strong> Hydrogen bondOHOIPhR 3 SnHO 2))) 0-20 o COPhNakamura, E. JACS, 1991, 898084%<strong>The</strong> radical nature of some reactions is compromised by attached R groupsHOPOROR+R'R'NR')))R'R'R'HNOPOR ORHubert C. etalJOC, 1995, 1488>90% yield <strong>in</strong> 1.5 h w/ R = EtNo rate enhancement w/ R = C 16 H 31Sonolysis of Iron CarbonylsOOOHFe 2 (CO) 9)))23 o C, 30 m<strong>in</strong>(OC) 3 FeO60 atm COOOLey, S.V etal.J. Organomet. Chem.1985, C17, 28570%Milder Conditions, Enhanced Rates for the Heck Reaction (Cheng, J etal. Bull. Inst. Chem. Acad. S<strong>in</strong>. 1989, 9)ICO 2 MePd(PPh 3 ), NEt 3CH 3 CN, C 6 H 6CO 2 Me50 o C, 6h, 76% (sonication)80 o C, 24h, 71% (thermal)Pauson-Khand Annulation is Accelerated by Sonication (J. Organomet. Chem. 1988, 233)OCo(CO) 3HCo(CO) 3+OBu 3 PO, hexane)))Ph
CARBON-CARBON BOND FORMATIONHorner-Wadsworth-WittigO H 3 CO 2 SOPORORCH 3))) THF, 23 o CSO 2 CH 3CH 370-80%
Saponifications <strong>in</strong> Aqueous Solutions are Enhanced by Ultrasound; Sonochemical EmulsificationOOMe10% aq. NaOHOOHTL, 1979, 3917Reflux, 90 m<strong>in</strong>, 15%Sonication, 23 o C, 96%Formation of anions from heterogenous bases facilitated by sonicationSONaH,)))50 o C, 1h SNaTL, 1966, 6383OCNCO 2 EtBrBrK 2 CO 3, )))PEG-600, ClCH 2 CH 2 ClCNCO 2 EtCh<strong>in</strong>. Chem. Lett. 1991, 517Chem. Abstr. 1992, 116, 193753t85%Nitrogen Protection (Under Phase Transfer Catalysis) Is Enhanced. This is also true for <strong>in</strong>dole protection.NHOH(t-BuOCO) 2 O, NaHCO 3MeOH, ))), 3hNCOOt-BuOHLuche, J.L. etal. Synlett, 1991, 37>80% yieldA Case for "C-H Functionalization"? (JCSCC, 1994, 1425)SiNaNO 2 , AcOHCe(NH 4 ) 2 (NO 3 ) 6CHCl 3 , 23-75 o C))), 4hSiNO 2[O]Si+HNO 2SiNO2REDUCTION REACTIONSMeOBrLAH, DME))), 35 o C, 7hMeO70%Boudjouk etal. TL, 1982, 1643OSiOMeLiAlD 4 , C 6 D 12))), 25 o C, 2hOSiDTL, 1984, 1415• <strong>The</strong> usual reductive protocols <strong>in</strong>volv<strong>in</strong>g heterogenous systems are also facilitated(e.g., nitro to am<strong>in</strong>e, aldehyde to alcohol etc)• Generally, sonochemical reduction chemistry is underexplored
OXIDATION REACTIONSPerfluoroalkylO 2 , Sulfonate salt)))OHMokryi, E.N etal. Akad. Nauk Ukr. 1993, 7, 99Chem. Abstr. 1994, 121, 107751KMnO 4 , H 3 O +PhH,450 torr)))OJCS Perk<strong>in</strong> Trans. II, 1988, 375HORRTPAP, NMO25 o C, 90 m<strong>in</strong>O>90%RORTL, 1991, 3201OHPCC/SiO 220 m<strong>in</strong>, )))OJOC, 1989, 5387ORGANOMETALLIC SONOCHEMISTRY•This has seen the greatest impact <strong>in</strong> terms of sonochemical <strong>applications</strong>•Usually, the <strong>in</strong>fluence of <strong>ultrasound</strong> is to remove passivat<strong>in</strong>g coat<strong>in</strong>gs on metals (oxides, carbonates, OH etc) -->Depassivation and also to aid <strong>in</strong> s<strong>in</strong>gle electron transfer processes which constitute a crucial step <strong>in</strong> the formation oforganometallic compounds•Recently Reviewed: Luche, J.L.; C<strong>in</strong>tas, P. (Furstner, A. (ed.)), Activated Metals, VCH, We<strong>in</strong>heim, 1997.ALKALI METALS AND MAGNESIUMBogdanovic etal. ACIEE, 1983, 728+ Mg))) )))+Mg*Acylo<strong>in</strong> Condensation (SynLett, 1990, 89)CO 2 EtMe 3 SiCl, Na, THFMgOSiMe 3Activated Mg* is useful forGrignard reagent prepSONICATION IS GENERALLY USEFULFOR GRIGNARD REACTIONS, HALOGEN-METAL AND TRANSMETAL EXCHANGESCO 2 Et0 o C, 2 h, ))), 82%OSiMe 3OHO90%, <strong>The</strong>rmalNR 2Li, THFOTL, 1988, 218390%, Sonochemical
• Historically, the first metal to be used <strong>in</strong> <strong>organic</strong> chemistryREACTIONS WITH ZINC METAL• Zn-mediated reactions have been the most extensively studied <strong>in</strong> sonochemical organometallic chemistryREDUCTIONS<strong>The</strong> Zn(Ni) Couple (Luche, J.L. etal. JOC, 1989, 5313OZn(Ni) (9:1)EtOH, H 2 OOZn(Ni) (9:1)EtOH, H 2 OO95 %NH 3 -NH 4 ClpH 8,))), 1.5 h23 o C))), 3 h, 23 o C96 %<strong>The</strong>rmal (12 h, 90 %) <strong>The</strong>rmal (24 h, 90 %)TL, 1993, 1993, 357OOOZn, AcOH, 25 o C10 m<strong>in</strong>, 100 %)))H5!:5" =1.5:1ORGANOZINC REAGENTSImproved Simmons-Smith Protocol (TL, 1982, 2729)Zn, CH 2 I 2 , DME4h, 90 o C,)))67% (12 % <strong>The</strong>rmally)Unpredictable <strong>in</strong>duction period suppressedHydroperfluoroalkylation/ Carbometallation (JACS, 1985, 5186)CF 3 I+HOZn, CuI, THFF 3 C23 o C, 2 h, ))) 61 %OHBarbier-Type Processes (Boudjouk etal. JOC, 1982, 751)BrBrRR'Zn, Dioxane)))67-89%RRNo Reaction <strong>The</strong>rmally!R is electron withdraw<strong>in</strong>g
REFORMATSKY REACTION• Significant rate and yield improvements have been observedMeyers, A.I. JOC, 1991, 2091NOZn(Ag), THFNONRNCBr40 o C, ))), 2 hNR84 %NH 2Jackson etal. JOC, 1992, 3397INHBOCCOOBnZn(Cu), )))DMA, PhH, 30 m<strong>in</strong>IZnNHBOCCOOBn(Ph 3 P) 2 PdCl 2 , )))NNHBocCOOBnNBr• Sn and In seem to predom<strong>in</strong>ateAQUEOUS ORGANOMETALLIC COUPLINGSWhitesides, G.M. JOC, 1993, 5500Aq. CH 2 O +BrSn, aq. NH 4 Cl-THF23 o C, 1 h, )))HO60 %B<strong>in</strong>der etal. Tetrahedron, 1994, 749HOHOOOHOHAllylBr, Sn, )))EtOH-H 2 O (10:1)OH OHOH OH OH60 - 65 %OOCHOAllylBr, In, )))EtOH, 1 hOOOH60 %
OTHER METALS FOR ORGANOMETALLIC SONOCHEMISTRYCu for Ullmann Coupl<strong>in</strong>gs (Mason etal. Ultrasonics, 1986, 292)NO 2NO 2ONO 2Cu, DMFI))), 60 o C, 90 m<strong>in</strong>95 %Al for Reduction Chemistry (TL, 1993, 353)OHOHOOAl(Hg),10 % aq. HCOONaEtOH, 23 o C, )))OHHOHO80 %(<strong>The</strong>rmally 23 %)CONCLUSIONS• Sonochemistry is ga<strong>in</strong><strong>in</strong>g significance based on laboratory results and the availability of scale-up systems• Sonochemical <strong>applications</strong> can be envisaged <strong>in</strong> all types of systems, <strong>in</strong>clud<strong>in</strong>g homogenous reactions• Wide acceptance has been ga<strong>in</strong>ed at a practical/empirical level, however, the theoretical understand<strong>in</strong>g still lagssignificantly beh<strong>in</strong>d• <strong>The</strong> usefulness of <strong>sonochemistry</strong> cont<strong>in</strong>ues to expand <strong>in</strong>to the arena of electrochemistry, photochemistry andbiotechnology• FOR THE ORGANIC CHEMIST: WHEN IN DOUBT, SONICATE!!!!!Useful referencesPrice, G.J. (ed.)., Current Trends <strong>in</strong> Sonochemistry, Royal Society of Chemistry, Oxford, 1993Mason, T.J. (ed.), Chemistry With Ultrasound, Elsevier Applied Science, London, New York, 1990van Eldik, R.; Hubbard, C.D. (eds.), Chemistry Under Extreme or Non-Classical Conditions, Spektrum/Wiley, 1997Abdulla, R.F. Adrichimica Acta 21, 1988, 31 - 42