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Accounts of Chemical Research, 31, 4, pp. 159-162, 1998-04-21
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A radical account of "oxygenated Fenton chemistry"
MacFaul, Philip A.; Wayner, Danial; Ingold, Keith
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A Radical Account of
“Oxygenated Fenton
Chemistry”
1
In a recen t Accou n t, Sawyer et al.3h ave su m m arized m u ch of th eir earlier work on wh at th ey refer to as “oxygen ated Fen ton ch em istry”. Th e overall reaction is p erfectly straigh -forward an d n on con troversial. In th e p resen ce of d ioxy-gen , a m ixtu re con tain in g an iron catalyst (ioxy-gen erally FeII), Me3COOH (or H2O2), an d a h yd rocarb on in aceton itrile at room tem p eratu re yield s m ain ly th e keton e d erived from th e h yd rocarb on togeth er with sm aller qu an tities of oth er oxid a-tion p rod u cts su ch as th e corresp on d in g alcoh ol. Th e p rop osed m ech an ism for th ese oxid ation s is an yth in g b u t straigh tforward an d d eserves to b e ch allen ged . Th e m ost rem arkab le claim3 is th at “Fen ton reagen ts do n ot produ ce [Sawyer’s italics]... free carb on rad icals...”.4 Th is ign ores a wealth of earlier work on iron / h yd rop eroxid e/ h yd rocarb on ch em istry.7 Moreover, it also ign ores classical free rad ical an d au toxid ation ch em istry8wh ich we d em on strate h erein , b y m ean s of a few carefu lly selected exp erim en ts, p rovid e b oth a sim p ler reaction m ech an ism an d on e in con cord an ce with k n ow n free rad ical kin etics. Th is (classical) m ech an ism is sh own in ab b reviated form in reaction s 1-5 and will be fu rth er elab orated wh en n ecessary.
To d istin gu ish b etween Sawyer’s n on rad ical m ech an ism an d reaction s 1-5, we have utilized four of his catalysts, viz. ferric ch loride (FeIIICl
3, 1), iron (II) tetrakis(trip h en ylp h osp h in e oxid e) (FeII(OPPh
3)4, 2), iron (II) b is(2,2′-b ip yrid yl) (FeII(b p y)2,
3), an d iron (II) b is(p icolin ate) (FeII(PA)
2, 4), an d th ree of h is su b strates, viz. cycloh exan e, eth ylb en zen e, an d cycloh exen e. Reaction s were ru n in du plicate with con stan t stirrin g at room tem p eratu re u n d er 1 atm of oxygen for 18 h (th e con d ition s given in th e origin al rep ort9sin ce th ere is little reaction with cycloh exan e after th e 3 h in d icated in Tab le 2 of th e Accou n t3). Th e reagen t con cen tration s were also th e sam e as th ose em p loyed in som e of th e p reviou s work,3,9viz. 1.0 M h yd rocarb on , 10 m M catalyst, an d 20 m M Me3COOH (TBHP) or 20 m M Ph CH2CMe2OOH (MPPH, see b elow). Th e solven ts were aceton itrile (1 an d 3), p yrid in e/ aceton itrile (1:4 m ole ratio) (2), an d p yrid in e/ acetic acid (2:1 m ole ratio) (4) as d escrib ed origin ally.9 Reaction s were q u en ch ed with an
excess of trip h en ylp h osp h in e (to con vert h yd rop eroxid es to th e corresp on d in g alcoh ols) an d an alyzed on a Hewlett-Packard 5890 Series II gas ch rom atograp h (HP Ultra 1 cross-lin ked m eth yl silicon e colu m n , 12m × 0.2 m m × 0.33 µm ; tem p eratu re p rogram : 40°C for 7 m in , 15°C/ m in to 250°C, 250°C for 5 m in ) u sin g 1,4-d ib rom ob en zen e as an in tern al stan dard. Data an alyses were p erform ed u sin g an HP Ch em -station .. Th e ab solu te p rod u ct yield s10 are sh own in b ar grap h form in Figu re 1.
By exam in in g first th e 12 b ar grap h s from th e TBHP exp erim en ts, it is clear th at th e total p rod u ct yield in creases alon g th e series: cycloh exan e< ethylbenzene < cyclohexene an d th at, with a few excep tion s, th e total yield s for each su b strate are rou gh ly in d ep en d en t of th e catalyst. With cycloh exan e th e p rod u ct yield s are less th an or eq u al to th at of th e in itial catalyst, viz., 10 m M (overall average from ou r eigh t exp erim en ts ) 7.5 vs 10 m M from Sawyer’s et al.’s origin al fou r exp erim en ts9), with eth ylb en zen e th e average p rod u ct yield rises to 25.6 m M (vs 39.8 m M9) an d with cycloh exen e to 86.0 m M (vs 107.9 m M9). It is totally u n
-n ecessary to i-n vok e catalyst “tu r-n over” to explai-n th ese resu lts sin ce th ey can be sim ply accou n ted for on th e basis of th e relative im portan ce of reaction 5. For cycloh exan e,11eth yl-b en zen e,12an d cycloh exen e,12th e valu es for k
5are 0.048, 1.1, an d 6.1 M-1s-1, resp ectively. Th u s, reaction 5 is in sign ifican t for cycloh exan e, is relevan t for eth ylb en zen e, an d b ecom es im p ortan t for cycloh exen e. We can m ake a rou gh correction for h yd rocarb on oxid ation via tert-b u toxyl rad icals (reaction 2) b y su b tractin g th e average p rod u ct yield for cycloh exan e (7.5 m M) from th e average p rod u ct yield s for cycloh exen e (86.1 m M) an d eth ylben zen e (25.6 m M). With th is correction , th e ratio of cycloh exen e/ eth ylb en zen e p rod u cts wh ich p rob -ab ly arise m ain ly from au toxid ation , i.e. h yd rogen atom ab straction b y p eroxyl rad icals (reaction 5), is (86.1-7.5)/ (25.6-7.5) ) 4.3 (vs 3.3 from the original work9). Th e ratio of 4.3 is in rath er satisfactory agreem en t with th e ratio exp ected on th e b asis of th e relative m agn itu d es of th e k5 valu es for cycloh exen e an d eth ylb en zen e, viz.126.1/ 1.1) 5.5. We in trod u ced MPPH as a m ech an istic p rob e13 in tertalkyl h yd rop eroxid e/ iron catalyst/ alkan e system s to d istin
-Cycloh exan e
FeII+ Me3COOH f FeIII+ Me3CO•+-OH (1)
Me3CO•+ >CH2f Me3COH+ >C4H (2)
>C4H + O2f >CHOO• (3)
>CHOO•+ radical•f
>CdO (m ain)(+ >CHOH + >CHOOCMe3+ O2) (4)
Eth ylb en zen e an d Cycloh exen e
>CHOO•+ >CH2f >CHOOH + >C4H (5)
FIGURE 1. Oxidation of cyclohexane, ethylbenzene, and
cyclohex-ene by iron catalysts 1-4 and two tert-alkyl hydroperoxides, TBHP and M PPH, at room temperature under an atmosphere of oxygen for 18 h.
gu ish b etween alkan e oxid ation s via h igh -valen t iron-oxo sp ecies (as favored b y m an y oth ers) an d oxid ation s wh ich occu rred via h yd rogen atom ab straction from th e alkan e b y freely d iffu sin g alkoxyl rad icals; i.e., to d istin gu ish b etween th e reaction p ath way 6, 7 an d p ath way 8, 9 (wh ere Fenis FeII or FeIII).
Th e p rob e h yd rop eroxid e, MPPH, relies on th e fact th at β-scission of th e corresp on d in g tert-alkoxyl rad ical, reaction 10,
is m u ch too rap id (k10 ∼ 2 × 108 s-1) for th ere to b e an y h yd rogen atom ab straction from cycloh exan e (even at 1 M) an alogou s to reaction s 2 an d 9 (k2 ) k9 ) 1.2 × 106 M-1 s-1).14,15 Th u s, if th e reaction p roceed s via a m etal-b ased oxid an t (reaction s 6 an d 7), th e p rod u ct p rofile will b e u n affected b y th e u se of MPPH sin ce we h ave d em on strated th at in gen u in e 2-electron alken e oxid ation s MPPH is a p erfectly com p eten t su b stitu te for TBHP (in fact, th e ep oxi-d ation s of cycloh exen e an oxi-d cis-stilb en e were m ore efficien t with MPPH th an with TBHP).18 On th e oth er h an d , if th e reaction p roceed s via alkoxyl rad ical in term ed iates (reaction s 8 an d 9), th e very fastβ-cleavage of Ph CH2CMe2O•will lead p red om in an tly to b en zyl rad ical d erived p rod u cts. We h ave alread y ap p lied th e MPPH p rob e to a variety of h yd rop erox-ide/ iron / alkan e system s fin din g on ly alkoxyl radical ch em istry
in all cases.19 Con seq u en tly, it was n o su rp rise to d iscover th at th ere were essen tially n o cycloh exan e oxidation p rodu cts wh en MPPH was u sed in p lace of TBHP, th e m ain p rod u cts b ein g b en zald eh yd e (average yield 5.8 m M, ran ge 3.4-9.0 m M) togeth er with som e b en zyl alcoh ol (average yield 1.1 m M, ran ge 04.3 m M). These two com pounds are presum -ab ly form ed via reaction s 10, 11, an d 12.
In d ram atic con trast, th e MPPH-in d u ced oxid ation of eth yl-b en zen e an d cycloh exen e gave su yl-b stan tial q u an tities of th e corresp on din g keton es an d alcoh ols (Figu re 1).20 We attribu te th ese p rod u cts to au toxid ation of th ese two h yd rocarb on s in itiated b y th e b en zylp eroxyl rad icals, viz.
Fu rth er eviden ce th at th e ch em istry in qu estion is in itiated b y alkoxyl rad icals (reaction s 1 an d 2) was ob tain ed b y th e ad d ition of two com m ercially im p ortan t rad ical trap p in g an tioxid an ts, 2,6-d i-tert-b u tyl-4-m eth ylp h en ol (BHT) an d d ip h en ylam in e to oth erwise “n orm al” system s con tain in g 1.0 M eth ylb en zen e (EtPh ), 20 m M TBHP, or 20 m M MPPH an d 10 m M catalyst. Both of th ese an tioxid an ts, AH, react rap id ly with alkoxyl rad icals (k14BHT) 2.0 × 107M-1s-1,13k14Ph2NH) 3 × 108 M-1 s-1,21) an d with alkylp eroxyl rad icals (k
15BHT)
1.4 × 104M-1s-1,22k
15Ph2NH≈ 4 × 104M-1s-1,23). Kn owledge
of th ese an tioxid ative rate con stan ts lead s d irectly to th ree sim p le p red iction s. First, 100 m M Ph2NH sh ou ld com p letely in h ib it th e MPPH-p rom oted oxid ation s of EtPh b y trap p in g all th e b en zylp eroxyl rad icals form ed in reaction s 10 an d 11 b efore th ey can attack th e h yd rocarb on , reaction 13, i.e.
k15Ph2NH[Ph2NH] () 4 × 104 x 0.1 ) 4 × 103 s-1) . k13EtPh -[EtPh ] () 1.1 × 1.0 ) 1.1 s-1). Th is p red iction was con firm ed exp erim en tally with all fou r catalysts (see Figu re 2).24 Al-th ou gh BHT is on ly on e-Al-th ird as active as Ph2NH in trap p in g p eroxyl rad icals, even 20 m M BHT was su fficien t to in h ib it th e MPPH-p rom oted oxid ation of EtPh very stron gly (Figu re 2).24 Th e secon d p red iction is th at 20 m M an d 50 m M BHT sh ou ld p rovid e on ly p artial in h ib ition of th e tert-b u toxyl rad ical in itiated oxid ation of EtPh sin ce even 50 m M BHT can in tercep t on ly ca. 50% of th e tert-b u toxyl rad icals form ed in reaction 1, i.e. k14BHT[BHT] () (2.0 × 107) × 0.05 ) 1.0 × 106s-1) ≈ k2EtPh[EtPh ] () (1.05 × 106) × 1.0 ) 1.05 × 106s-1). Th e fin al p red iction is th at 100 m M d ip h en ylam in e sh ou ld p rod u ce alm ost com p lete in h ib ition of EtPh oxid ation p ro-m oted b y TBHP, i.e. k14Ph2NH[Ph2NH]) (3 × 108) × 0.1 ) 3 × 107s-1. Th e valid ity of th e secon d an d th ird p red iction s are also attested to b y th e d ata sh own in Figu re 2.24
Ou r resu lts p rovid e u n eq u ivocal p roof th at Sawyer’s “oxygen ated Fen ton ch em istry” in organ ic solven ts (an d b y im p lication in water) in volves sim p le free-rad ical-m ed iated ch em istry. It is n ot rad ical-free as Sawyer h as su ggested .3,9 Th ere are, of cou rse, n u m erou s en zym es, in clu d in g cyto-ch rom e P450s an d m eth an e m on oxygen ases, wh icyto-ch can effect alkan e oxidation s via h igh -valen t iron-oxo species. However, m im ickin g th ese en zym e with sim p le ch em ical system s is n ot a trivial u n d ertakin g an d , to ou r kn owled ge, h as n ever b een ach ieved with an iron catalyst an d a tertiary alkyl h yd rop er-oxid e.27 We con clu d e th at m ech an istic in terp retation in th is gen eral area of b iom im etic ch em istry sh ou ld on ly b e d rawn after exh au stive stu d ies u sin g a variety of exp erim en tal tests for th e in volvem en t of free rad icals.7,13,19,25-27
RtOOH+ Fenf RtOH+ Fen+2dO (6) Fen+2dO + RH f Fen+ ROH (7) RtOOH+ Fenf RtO•+ Fen+1OH (8) RtO•+ RH f RtOH+ R•98 O2 ROO•f p rod u cts (9) Ph CH2CMe2O•f Ph CH2•+ Me2CO (10) Ph CH2•+ O2f Ph CH2OO• (11) 2Ph CH2OO•f Ph CHO + Ph CH2OH+ O2 (12) Ph CH2OO•+ >CH2f Ph CH2OOH + >C4H (13)
FIGURE 2. Effect of adding antioxidants to the oxidation of
ethylbenzene by iron catalysts 1-4 and TBHP or M PPH at room temberature under an atmosphere of oxygen for 18 h.
RO•+ AH f ROH + A• (14) ROO•+ AH f ROOH + A• (15)
Commentary
W e th an k th e Association for In tern ation al Can cer Research an d th e N ation al Fou n dation for Can cer Research for partial su pport of th is w ork .
Philip A. MacFaul,2D. D. M. Wayner, and K. U. Ingold*
Steacie In stitu te for Molecu lar Scien ces, Nation al Research Cou n cil of Can ad a, Ottawa, On tario, Can ad a K1A 0R6
References
(1) Issu ed as NRCC No. 40851.
(2) NRCC Research Associate, 1995-1997.
(3) Sawyer, D. T.; Sob kowiak, A.; Matsu sh ita, T. Acc.
Ch em . Res 1996, 29, 409-416.
(4) Sawyer’s n on rad ical m ech an ism in volves in itial form ation of a p eroxy-iron(II) species (form ulated as [FeIIOOR] ign orin g th e oth er ligan d s) wh ich th en reacts with O2to form an oth er (q u ote) “h ypoth
eti-cal” in term ed iate, [FeIIIOOR(O
2)], wh ich su b se-qu en tly oxid izes alkan es to keton es. (Peroxy-iron-(III) com p lexes are well estab lish ed .5 However, at least som e of th em h ave b een d em on strated n ot to react directly with h yd rocarb on s.5a,6)
(5) See, e.g.: (a) Barton , D. H. R.; Be´vie`re, S. D.; Ch avasiri, W.; Doller, D.; Liu , W.-G.; Reib en sp ies, J. H. N ew . J. Ch em . 1992, 16, 1019-1029 and refer-en ces cited . (b ) Me´n age, S.; Wilkin son , E. C.; Qu e, L., Jr.; Fon tecave, M. An gew Ch em ., In t. Ed. En gl.
1995, 34, 203-205.
(6) Un p u blish ed stop -flow exp erim en ts from th is labo-ratory.
(7) See accom p an yin g com m en t b y Professor Ch eves Wallin g.
(8) Wallin g, C. Free Radicals in Solu tion ; Wiley: New York, 1957.
(9) Kan g, C.; Red m an , C.; Cep ak, V.; Sawyer, D. T.
Bioorg. Med. Ch em . 1993, 1, 125-140.
(10) (a) Oxid ation of cycloh exan e (1 M) b y iron catalysts (10 m M) an d alkyl h yd rop eroxid es (20 m M) u n d er an atm osp h ere of oxygen . Prod u ct yield s (m M) are from d u p licate exp erim en ts; resu lts in b rackets are from Tab le 3 in ref 9. (i) TBHP. Catalyst, keton e, alcoh ol, m ixed p eroxid e: 1, 2.7, 3.4 (4.8); 4.2, 4.7 (4.2); 0.2, trace, (0). 2, 3.2, 3.9 (4.3); 1.3, 1.3 (6.1); 0, 0 (0). 3, 2.9, 4.4 (3.7); 2.6, 3.4 (4.9); 0, 0 (0). 4, 10.9, 10.7 (12); 0, 0 (0); trace, 0 (0). (ii) MPPH. Catalyst, keton e, alcoh ol, m ixed p eroxid e, b en zald eh yd e, b en zyl alcoh ol, b ib en zyl, MPPOH: 1, 0.5, 0.5; 0.9, 0.5; 0, 0; 3.8, 3.4; 4.3, 3.2; trace, trace; 0.5, 0.8. 2, 0, 0; 0, 0; 0, 0; 4.5, 6.0; 0, 0; 0, 0; 3.3, 3.5. 3, 0, 0; 0, 0; 0, 0; 5.7, 5.0; 0.4, 0; 0, 0; 0.3, trace. 4, 0, 0; 0, 0; 0, 0; 9.0, 8.7; 0.3, 0.5; 0, 0; 0.6, 0.8. (b ) Oxid ation of cycloh exen e (1 M) b y iron catalysts (10 m M) an d alkyl h ydrop eroxides (20 m M) u n der an atm osp h ere of oxygen . Prod u ct yield s (m M) are from d u p licate exp erim en ts; resu lts in b rackets are from Tab le 3 in ref 9. (i) TBHP. Catalyst, keton e, alcoh ol, ep oxide, m ixed p eroxid e: 1, 14.4, 19.9 (71); 32.7, 45.5 (69); 0.3, 0.2 (0); 0.3, 0.4 (0.5). 2, 34.1, 71.5 (60); 2.8, 6.5 (35); 0, 0 (0); 0.2, 0 (0.5). 3, 112.5, 89.5 (86); 70.0, 59.2 (60); 6.0, 4.4 (0); trace, 0 (1.8). 4, 49.5, 64.6 (45); 1.5, 2.1 (2.2); 0, 0 (0); 0, 0 (0.5). (ii) MPPH. Catalyst, keton e, alcoh ol, ep oxid e, m ixed p eroxid e, b en zal-d eh yzal-d e, b en zyl alcoh ol, b ib en zyl, MPPOH: 1, 27.7, 27.0; 49.3, 75.0; 0, 0; 0, 0; 0.1, 0; 1.3, 1.5; 0.4, 0.2; 0, 0. 2, 142.5, 168.0; 10.3, 10.7; 2.0, 2.1; 0, 0; 0, 0; trace, trace; 0, 0; 0, 0. 3, 103.9, 65.9; 82.5, 59.6; 2.0, 0.6; 0, 0; 0, 0; 4.2, 2.7; trace, 0.3; 0, 0. 4, 145.0, 158.5; 7.0, 7.5; trace, trace; 0, 0; 0, 0; 0, 0; 0, 0; 0, 0. (c) Oxidation of eth ylben zen e (1 M) by iron catalysts (10 m M) an d
alkyl h ydrop eroxides (20 m M) u n der an atm osp h ere of oxygen . Prod u ct yield s (m M) from d u p licate exp erim en ts, resu lts in b rackets are from Tab le 3 in ref 9. (i) TBHP. Catalyst, keton e, alcoh ol, m ixed p eroxid e: 1, 20.4, 18.7 (16); 10.7, 9.0 (9.2); 0, 0 (0).
2, 18.5, 25.1 (38); 4.5, 0.6 (16); 0, 0 (0). 3, 14.5, 13.1 (35); 11.1, 9.4 (11); 0, 0 (0). 3+ 10 m M benzaldehyde ad d ed p rior to th e ad d ition of TBHP (7.0 m M an d 5.3 m M b en zald eh yd e recovered in th e d u p licate exp erim en ts), 14.6, 13.0; 38.2, 36.5; 1.1, 1.0. 4, 28.4, 26.3 (34); 3.4, 3.1 (0); 0, 0 (0). (ii) MPPH. catalyst, keton e, alcoh ol, m ixed p eroxid e, b en zald eh yd e, b en zyl alcoh ol, b ib en zyl, MPPOH: 1, 35.4, 52.8; 19.8, 23.2; 0, 0; 0.15, trace; 0.9, 1.0; 0, trace; 0, 0.6.
2, 69.1, 46.1; 1.4, 9.5; 0, 0; trace, 0; 0, 0; 0, 0; 0, 0. 3, 52.6, 40.2; 16.8, 22.4; 0, 0; 0, 0; 1.2, 1.5; 0, 0; 0.8, 1.0.
4, 90.9, 78.8; 7.8, 4.5; 0, 0; 0, 0; 0, 0; 0, 0; 0, 0. (11) Korcek, S.; Ch en ier, J. H. B.; Howard , J. A.; In gold ,
K. U. Can . J. Ch em . 1972, 50, 2285-2297.
(12) Howard , J. A.; In gold , K. U. Can . J. Ch em . 1966, 44, 1119-1130.
(13) Aren d s, I. W. C. E.; In gold , K. U.; Wayn er, D. D. M.
J. Am . Ch em . Soc. 1995, 117, 4710-4711.
(14) Avila, D. V.; Brown , C. E.; In gold , K. U.; Lu sztyk, J.
J. Am . Ch em . Soc. 1993, 115, 466-470.
(15) Th e corresp on d in g k2(k9) valu es for eth ylb en zen e an d cycloh exen e are 1.05 × 106an d 5.7 × 106M-1 s-1, resp ectively.16Hyd rogen atom ab straction from th e h yd rop eroxid e b y th e alkoxyl rad ical (k) 8.7 × 106 M-1s-1 in CH3CN)17 can b e ign ored in th ese system s b ecau se of th e low h yd rop eroxid e con cen -tration s em p loyed .
(16) Pau l, H.; Sm all, R. D., Jr.; Scaian o, J. C. J. Am . Ch em .
Soc. 1978, 100, 4520-4527.
(17) Avila, D. V.; In gold , K. U.; Lu sztyk, J.; Green , W. H.; Procop io, D. R. J. Am . Ch em . Soc. 1995, 117, 2929 -2930.
(18) Old royd , R. D.; MacFau l, P. A.; Masch m eyer, T.; Th om as, J. M.; Sn elgrove, D. W.; In gold , K. U.; Wayn er, D. D. M. An gew . Ch em ., In t. Ed. En gl. 1996,
35, 2787-2790.
(19) Sn elgrove, D. W.; MacFau l, P. A.; In gold , K. U.; Wayn er, D. D. M. Tetrah edron Lett. 1996, 37, 823-826. Aren d s, I. W. C. E.; MacFau l, P. A.; Sn elgrove, D. W.; In gold , K. U.; Wayn er, D. D. M. N ATO ASI
Con feren ce, 1996. MacFau l, P. A.; Aren d s, I. W. C.
E.; In gold , K. U.; Wayn er, D. D. M. J. Ch em . Soc.,
Perk in Tran s. 2 1997, 135-145. MacFaul, P. A.;
In gold , K. U.; Wayn er, D. D. M.; Qu e, L., Jr. J. Am .
Ch em . Soc. 1997, 119, 10594-10598.
(20) For eth ylben zen e, Ph CHO average yield) 0.02 m M, ran ge 0-0.15 m M, PhCH2OH average yield (after worku p in th e u su al way13,19 with Ph
3P to red u ce h yd rop eroxid es to alcoh ols) 0.6 m M, ran ge 0-1.5 m M. For cycloh exen e, th e corresp on d in g valu es are 0.01, 0-0.1, 1.5, and 0-4.2 m M. The sm all yields of b en zald eh yd e in th ese reaction s are d u e to its oxid ation as was d em on strated b y th e p artial d e-stru ction of ad d ed b en zald eh yd e d u rin g th e 3/ Me3COOH-in d u ced oxid ation of eth ylb en zen e (see ref 10).
(21) MacFau l, P. A.; In gold , K. U.; Lu sztyk, J. J. Org.
Ch em . 1996, 61, 1316-1321.
(22) Bu rton , G. W.; Dob a, T.; Gab e, E. J.; Hu gh es, L.; Lee, F. L.; Prasad , L.; In gold , K. U. J. Am . Ch em . Soc.
1985, 107, 7053-7065.
(23) Brown lie, I. T.; In gold , K. U. Can . J. Ch em . 1967,
48, 2419-2425.
(24) Th e effect of ad d in g an tioxid an ts (m ole p ercen t relative to su b strate) to th e oxid ation of eth ylb en -zen e (1 M) b y iron catalysts (10 m M) u n d er an
atm osp h ere of oxygen . Prod u ct yield s (m M) from du p licate exp erim en ts: (a) TBHP (20 m M). Catalyst, n o an tioxid an t, 2% BHT, 5% BHT, 10% Ph2NH: Keton e: 1, 20.4, 18.7; 3.4, 5.4; 0, 0; 0, 0. 2, 18.5, 25.1; 7.2, 9.5; 2.3, 3.2; 0.4, 1.4. 3, 14.5, 13.1; 5.8, 6.2; 5.9, 2.4; 0, 0. 4, 28.4, 26.3; 8.0, 7.8; 7.7, 6.4; 0, 0. Alcoh ol: 1, 10.7, 9.0; 10.4, 10.3; 4.8, 4.7; 0, 0. 2, 4.5, 0.6; 1.2, 0.3; 0, 0; 0, 0. 3, 11.1, 9.4; 6.2, 4.4; 4.9, 2.7; 1.1, 1.9. 4, 3.4, 3.1; 2.6, 1.0; 1.2, 0.8; 0.5, 0.1. (b ) MPPH (20 m M) + 2% BHT. Catalyst, ketone, alcohol, m ixed p eroxid e, b en zald eh yd e, b en zyl alcoh ol, b ib en zyl, MPPOH. 1, 2.6, 2.0; 2.7, 1.6; 0, 0; 2.2, 1.3; 1.8, 1.4; 0, 0; 2.8, 3.0. 2, 0.7, 5.8; 0, 0.2; 0, 0; 0.8, 1.7; 0, 0.1; 0, 0.4; 0.8, 2.0. 3, 1.4, trace; 0, 0; 0, 0; 1.6, 2.1; 0, 0; trace, 0; 4.1, 7.3. 4, 0.9, 1.2; 0, 2.0; 0, 0; 3.2, 2.8; 0, 0; 0, 0; 2.0, 2.0. (c) MPPH (20 m M)+ 10% Ph2NH. Catalyst, keton e, alcoh ol, m ixed p eroxid e, b en zald eh yd e, b en zyl alcoh ol, b ib en zyl, MPPOH: 1, 0, 0; 0, 0; 0, 0; 2.7, 2.7; 6.3, 6.4; trace, 0; 0.2, 0.2. 2, 0, 0; 0, 0; 0, 0; 12.1, 12.3; 0.4, 0; 0, 0; 0, 0. 3, 0, 0; 0, 0; 0, 0; 5.7, 6.0;
4.2, 4.3; 0, 0; 0.3, 0.2. 4, 0, 0; 0, 0; 0, 0; 11.5, 11.2; 0, 0; 0, 0; 0, 0.
(25) See, e.g., th e followin g stu d ies in n on aq u eou s system s: Grin staff, M. W.; Hill, M. G.; Lab in ger, J. A.; Gray, H. B. Scien ce 1994, 264, 1311-1313. Min isci, F.; Fon tan a, F.; Aran eo, S.; Recu p ero, F.; Zh ao, L. Syn lett 1996, 2, 119-125. Newcom b, M.; Sim akov, P. A.; Park, S.-U. Tetrah edron Lett. 1996,
37, 819-822.
(26) Peroxyl, alkoxyl, an d alkyl rad icals h ave even b een d etected b y ESR sp in -trap p in g d u rin g th e FeIIin -du ced decom p osition of TBHP in an organ ic solven t (CH2Cl2), see: Ian n on e, A.; Tom asi, A.; Can field , L. M. Rev. Ch em . In term ed. 1996, 22, 469-479. (27) In gold , K. U.; MacFau l, P. A. In Biom im etic
Oxida-tion s Catalyzed by Tran siOxida-tion Metal Com plexes;
Meu n ier, B., Ed .; Im p erial College Press: Lon d on , U.K., in p ress.
AR970057Z
Commentary
