Indian Journal of Chemi stry Vo l. 43B, May 2004, pp. 936-946

Mild and selective oxidation of and deoximation of oximes over supported quinolinium fluorochromate

G Abraham Rajkumar, V Si va muruga n, Banumathi Arabindoo & V Murugesan* Departmen t of Chem istry, Ann a Uni ve rsity, Chen nai 600025, Ind ia E- lIlail: v_lIlurllgll @!z ollllail.colll. Fax: +09/ -44-22200660

Recei ved 6 Septelllber 2002; accepted (revised) 29 lilly 2003

Quinolinium nuorochro mate supported over sili ca gel selec ti vely brin gs about th e ox idati on of a wide va riety of alco­ hols and ox idative deoximati on of cert ain aldox im es and ketox imes to th e corresponding carbonyl compounds in good yield. The reagent selec ti vely ox idises pri mary hydroxy l group in the presence of seconda ry hydroxy l group. The selec tivit y is also ex hi bited in the oxidati on of ax ial hydroxy l group of the cis-4-t-b utyl in preference to eq ui toria l hydroxyl group. Further th e reagent is stable even after a peri od of twelve weeks of it s storage. IPC: Int.CI.7 C 07 B 31/00, C 07 C 31100

Oxidati on is one of the most important reacti ons in th at there are a number of Cr(VI) reagen ts supported functi onal group transformati ons in sy ntheti c organi c on in ert solid supports. The supported Cr(V I) based chemi stry. The oxidati ve transformati on of alcohols into reagents can be broadl y categori sed as fo ll ows: aldehydes and ketones is of paramount importance in (1 ) Chromium triox ide supported on inert inorgani c 12a i organic chemistry both for laboratory scale ex periments supports. . and manufacturing processes. Though several reagents (2) Heterocyclic halochromates supported on inert .. l3a·d and methods are avail abl e, conti nuous attention is 1I1 0rganl c supports. drawn to newer and selective meth ods to accompli sh (3) Polymeric analogues of heterocyclic halochro­ thi s transformation. I Hexavalent chromium reagents are mates. 14a-d hi ghl y valuable ox idi sing agents fo r the ox id ati on of Though these reagents have advantages they cannot organic compounds? In the past, reagents such as Jones, be easil y prepared .1 2a.b.C. 14a.d Further they un dergo l2b e San-ett and Collins prepared fro m chromi c ac id and rapid deacti vation on storage . and large excess of chromium trioxide were wi dely used for the ox idation th e reagent I2b.C.13n-d is required bes ides longer reacti on of alcohols to the cOlTesponding carbonyl compounds.3-5 time.1 2g. 14b.d Thus, there still ex ists scope for an effec­ However, drastic reacti on conditi ons paved way for a ti ve, selecti ve and a stable supported Cr(VI) reagent new class of mild chromium (VI) reagents viz., to accompli sh th e ox idatio n of alcohols and related heterocyclic halochromates. ox idative transform ati ons. Corey and Suggs introdu ced pyri dinium chl oro­ In continuation of our investi gati ons on the utility chro mate (PCC) fo r the ox idati on of alcohols 6 of quinolinium flu orochromate supported on in ert in - Pyridinium flu orochro mate (PFC/, quinolinium organIC. support 13c., d we herell1· report t he preparatI.on chl orochromate (QCC)8, bipyridinium chl orochromate and syntheti c utili ty of quinolinium Ouorochro mate (BPCC)9 and quinolinium flu orochromate (QFC)IO".b supported on sili ca gel (QFC-sili ca gel) as a selec ti ve, are other notabl e halochromates. Though the hetero­ stabl e and versatile oxida nt in th e oxid ati on of alco­ cycli c halochromates were foun d to be better in their hols and ox id ati ve deox im ati on of certai n al dox imes reacti vity and selecti vity compared to the co mmon and ketox imes to the corresponding carbonyl com­ Cr(VI) oxidants, th eir utility is restri cted due to th e pounds. di ffi culty in product isolati on, low reacti vity, long reaction time and hi gh acidity. Results and Discussion The concept of supporting Cr(VI) based reagents Quinolinium tluorochromate supported on sil ica onto inert inorgani c and polymeric matrices has cir­ gel (QFC-sili ca gel) was prepared ill situ adopting th e cum vented some of the probl ems associated with procedu re simil ar to the preparati on of si lv er carbon­ 15 these reagents. II The survey of I iterature has revealed ate on celite. The average loading of the reagent was RAJKUMAR et al.: QFC-SILICA GEL AS A SELECTIVE, STATIC AND VERSATILE OXIDANT 937 found to be 1.4-1.5 millimoles of QFC per gram of silica gel. The effect of the solvent was evaluated by R1 carrying out the oxidation of benzyl (chosen OH QFC I SG . as model substrate) in a series of solvents of varying R2 >- polarity such as dichloromethane, chloroform, ben­ Scheme I zene, tetrahydrofuran and hexane. The maximum conversion of to benzaldehyde oc­ oxidation of primary alcohols with an alkyl group at curred in a shorter reaction period in hexane and di­ C-2 position such as 2-ethyl I-hexanol (lh) and chloromethane. Hence hexane was chosen as the sol­ (li) proceeds smoothly at a faster vent for most of the oxidation studies excepting for a rate than I-hexanol (lb) and I-pentanol (Ie). The re­ few cases in which dichloromethane was used. sults of the oxidation of alcohols are significant since The substrate/oxidant mole ratio was optimised by aliphatic alcohols either undergo overoxidation or carrying out a series of oxidation studies with a set of give a low yield of products. ' 6 It has been observed chosen alcohols. The oxidation of 10 millimoles of that the oxidation of secondary alcohols (3a-e) with each of I-heptanol, 2-, benzyl alcohol and QFC-silica gel proceeds smoothly only under reflux cyclohexanol with varying amounts of QFC-silica gel conditions resulting in high conversion of alcohols to at room temperature and under reflux conditions was the corresponding ketones. The results are given in carried out. The optimum substrate/oxidant mole ratio Table I. for these alcohols have been found to be 1: 1.25, 1: l.5, QFC-silica gel oxidises alicyclic alcohols in hexane 1:l.25 and l:l.S, respectively. (Table II) under reflux conditions to the correspond­ The oxidation of a series of aliphatic primary alco­ ing ketones in high yield. The observed order of reac­ hols with QFC-silica gel reveals that the lower homo­ tivity is > cycloheptanol > cyclooctanol logues up to l-octanol (la-Ie) are readily converted > cyclohexanol. The results are in accordance with the to the corresponding aldehydes at room temperature qualitative interpretation suggested by Brown et al. 17 while the higher homologues such as I-nonanol (If) on the basis of I strain in these rings. The oxidation of and I-decanol (lg) require reflux condition (-) menthol with QFC-silica gel gave exclusively (Scheme I). Further, it is interesting to note that the (-) menthone in 72% yield.

Table 1- Oxid ation* of aliphatic primary and seco ndary alcohols

Substrate R I R2 Substrate/Oxidant Product" Reaction Yi eld" . b mole ratio time (%) (hr)

la CH)(CH2)2 H I: l.25 2a 2 63

Ib CH3(CH2)3 H I: 1.25 2b 4 8 1

Ie CH)(CH2) 4 H I: 1.25 2c 5 79

Id CH3(CH2)s H I: 1.25 2d 6 83

Ie CH)(CH2) 6 H I: 1.25 2e 5 80

If CH)(CH2h H I: 1.25 2f 4 7 1'

Ig CH)(CH2)g H I: l.25 2g 4 86'

Ih CH)(CH2k CH-C2Hs H I: 1.25 2h 4 81 Ii (CHJ))C H I: 1.25 2i 2 79

3a (}H3 CH)CH2 I: 1.5 4a 2 64'

3b CH) CH)(CH 2) ) I: 1.5 4b 4 64'

3c CH) CH)(CH2)4 I: 1.5 4c 5 84'

3d CH) CH3(CH2)5 I: 1.5 4d 6 88'

3e CH3 CH3(CH2h 1:1.5 4e 3 83' "oxidation at room temperature and under reflux conditions; Solvent: Hexane ·confirmed by GC, IR and IH NMR; bdetermined by GC analysis "isolated yield 938 INDIAN J. CHEM., SEC B, MAY 2004

Table II-Oxidation * of alicyclic alcohols with QFC - silica gel

Substrate Substrate/ Product" Reaction Yield " b.p./m.p. Oxidant time b (%) (l it b.p./m.p.) mole ratio (hr) °C/mm Hg

OH 0 711130 6 1: 1.5 6 4 S5 (1 39/760)

OH 0 93/100 6 1: 1.5 6 7 71 (155/760) OH CH 0 95/100 1: 1.5 0c~ 4 77 0 ' (164/760)

OH 0

lOS/SO 1: 1.5 5 SO 6 6 (179/760)

OOH 40 (42) 1: 1.5 6.5 74 0° (m.p.)

C~ CH3

102/20 1: 1.5 2 72 6 0H 60 (210/760) ~ ~ H3C CH3 H3C C~

*oxidation under reflux conditions; Solvent : Hexane "confirmed by IR, IH NMR and GC analysis ; bdetermined by GC analysis Cisolated yield

Oxidation of benzyl alcohol with QFC-silica gel in the substrates with an electron withdrawing group in 2 hexane proceeded smoothly at room temperature or 4 position (Sb, dI, g). On the other hand, the differ- (Scheme II). However, the presence of a substituent on the aromatic ring has a significant effect in the re­ R'>-OH QFC/SG. action time and product yield. Thus, substrates with an electron releasing group in 2 or 4 position (Se, f, h) ROO were readily oxidised in a shorter reaction period than Scheme n RAJKUMAR et al.: QFC-SILICA GEL AS A SELECTIVE, STATIC AND VERSATILE OXIDANT 939

Table III-Oxidation* of aromatic primary and secondary alcohols

Substrate R' R" Substrate/Oxidant Product" Reaction Yieldc b mole ratio time (%) (hr)

Sa C6H5 H 1: 1.25 6a 2(2) 93(96) Sb 2-N02-C6H4 H I: 1.25 6b 4(4) 49(70) Se 3-NOr C6H4 H I: 1.25 6e 4(4) 56(75) Sd 4-NOrC6H4 H 1: 1.25 6d 4.5(4.5) 53(71 ) Se 2-CHr C6H4 H I: 1.25 6e 3(3) 68(88)

Sf 4-CH3-C6H4 H I: 1.25 6f 3(3) 74(90) Sg 4-CI-C6H4 H I: 1.25 6g 6(5) 48(74) Sh 4-CH30-C6H4 H 1: 1.25 6h 4(3) 76(95)

Si C6H5CH2 H 1: 1.25 6i 6(4) 82(90) 7a C6H5 CH) 1:1 .5 8a 7(4) 50(78) 7b C6H5 C6H5 1:1.5 8b 4.5(3) 59(89)

7e C6H5(CH)OH C6H5 1:1 .5 8e 3(3) 88(89) *oxidation at room temperature and under reflux conditions; Solvent: Hexane "confirmed by GC, IR and 'H NMR; bdetermined by GC and TLC analysis Cisolated yield; values in parentheses ( ) refer reaction time and yield obtained under reflux condi­ tion ence in reactivity between 2-phenyl (S i) and benzene under reflux condition gave cholest-4-en-3- benzyl alcohol suggests that QFC-silica gel has more one with cholest-5-en-3-one as the intermediate.18 affinity towards the oxidation of a primary side chain However, the oxidation of cholesterol with QFC-silica hydroxyl group attached to an aromatic ring with a gel gave exclusively cholest-5-en-3-one in 70% yield less number of spacer methylene groups. The results without any side product due to the isomerisation of are summarized in Table III. Among the aromatic the double bone\. On the other hand, for the oxidation secondary alcohols (Table III) the oxidation of benz­ of cholesterol with unsupported QFC, a ten-fold hydrol (7b) proceeded more readily at a faster rate excess of the reagent was required and the yield of than the oxidation of (±) I-phenyl ethanol (7a). cholest-5-en-3-one was low « 50%). The oxidati on Further the oxidation of benzoin (7c) to the corre­ of 3-~-cholestanol with QFC-silica gel gave sponding diketone benzil (8c) under ambient tempera­ cholestanone in 60% yield . These reactions clearl y ture and shorter reaction time is illustrative of the indicate the potential utility of QFC-silica gel in mildness of QFC - silica gel. biosynthesis. Further the utility of QFC-silica gel as a mild oxidising reagent is revealed in the oxidation of The oxidation of with QFC-silica 1,2,5,6-0-dicyclohexylidene a-D-glucofuranose to gel in hexane furnished exclusively cinnamaldehyde the corresponding ketone in 60% yield. The stability without the formation of either bond cleavage product of acid labile cyclic acetal groups towards QFC-silica such as benzaldehyde or side products such as epox­ gel oxidation conditions is noteworthy. QFC-silica gel ide. cis and trans-Hexen-l-ol afforded the respective is quite effective for the oxidation of heterocyclic cis and trans aldehydes in reasonable yield and thus alcohols also. Thus, furfurol was oxidised to furfural no cis-trans isomerization was observed. Further the in high yield. On the other hand the oxidation of 3- oxidation of citronellol gave citronellal in high yield pyridyl afforded 3-pyridyl carboxaldehyde (88%) without the formation of pulegone, which may in 65% yield along with 20% quinoline (due to ligand arise due to cationic cyclisation. The results are pre­ exchange). This is a significant result, since the sented in Table IV. oxidation of the same substrate with unsupported Oxidation of steroidal homoallylic alcohols is a QFC failed to give the aldehyde and led to an crucial step in the synthesis of most of the steroidal intractable black tarry deposit. The results are harmones. Oxidation of cholesterol with PCC in presented in Table V. 940 INDIAN 1. CHEM., SEC B, MAY 2004

Table IV - Oxidation* of unsaturated alcohols with QFC - silica gel

Reaction b.p.im.p. Substrate/Oxidant Yield c Substrate Product a time b (lit. b.p.im.p.) mole ratio (%) (hr) °C/mm Hg

141/30 ©-CH = CH-CHO 1: 1.5 ©-CH CH-CH OH 2 84 = 2 (248n60)

CH3

105/20 1:1.5 ,;:? CH 3 88 3 (207/760) H3C Lf% H3Cd

~CHO 37/8 ~ \:1 .5 i 672 H3C OH H3C ~ (37-38/8)

CHO 39/10 ~~OH 1:1.5 5' 622 H3C H3C~ / 50/30

2 50/30 (H ChC=CH--CH OH 1:15 (H ChC=CH--CHO 3' 46 3 2 3 ( J33-35n60) *Oxidation under reflux conditions; Solvent: Hexane; 'oxidation at room temperature; Solvent: Dichloromethane aconfirmed by GC, IR and 'H NMR; bdetermined by GC analysis; cisolated yield; 2determined by GC analysis

The oxidising ability and the selectivity of other ions R R such as perrnanganate have been studied extensi­ vely.'9.2o Metal supported heterocyclic perrnanganate, )=N-OH R)=O bis(pyridine)silver perrnanganate though selectively R' oxidises the alcohols, amines and oximes, it is relatively Scheme III unstable and rather expensive. The transition metals such as copper and zinc incorporated heterocyclic sensItive groups such as 4-methoxy benzaldoxime permanganates such as tetrakis(pyridine) copper (II) (9b), cinnamaldoxime (9c), salicylaldoxime (ge) and permanganate and tetrakis(pyridine) zinc (II) permanga­ 4-hydroxy acetophenone oxime (90 were al so nate have been reported?' The oxidants are highly smoothly converted to the corresponding carbonyl hygroscopic and zinc pemlanganate is also inflammable compounds in high yield (> 90%). The results which make them unsuitable for mild and clean (Table VI) of ox.idative deoximation are comparable oxidation process. The same authors introduced with that obtained with unsupported QFC and are bet­ 22 bis(2,2' -bipyridyl) copper(II) permanganate . 23 and ter than the results obtained with pce, pee, H20 2 and 24 26 found it is far superior than that of Mn02 with respect to trimethyl ammonium chlorochromate - Oxidation oxidizing ability and easy handling, but it cleaves the of oximes to the corresponding carbonyl compounds benzylic double bonds. has been reported by many workers 27 as oximes can In order to evaluate additional capabilities of QFC­ be prepared from non-carbonyl compounds. Because silica gel, its utility in oxidative deoximation was of the limited of the KMn04 in organic sol­ studied (Scheme III). Oxidative deoximation of aro­ vents it has to be activated by impreganation onto matic aldoximes and ketoximes with QFC-silica gel supports such as zeolite. But not all the zeolites con­ proceeded rapidly under reflux conditions in di­ vert oximes to carbonyl compounds. Sodium perio­ chloromethane and the carbonyl compounds were ob­ date and tetrabutylammonium periodate require man­ tained in a quantitative yield. However, aliphatic al­ ganese (III) tetra phenyl porphyrin catalyst for the doximes such as heptanaloxime failed to undergo the regeneration of carbonyl compounds from oximes at transformation. Aldoximes and ketoximes with acid room temperature.28 RAJ KUMAR et al. : QFC-SILICA GEL AS A SELECTIVE, STATIC AND VERSATILE OXIDANT 941

Table V - Oxidation * of heterocyclic, steroidal alcohols and carbohydrates with QFC-silica gel c Substrate Substrate/ Product' Reaction Yield b.p./m.p. b Oxidant time (%) (lit. b.p./m.p.) mole ratio (hr) °C/mm Hg

96/15 ODWH I: 1.5 OQfO 3 65 (95-97/15)

74/30 1:1.5 3 1 79 GOWH Gc~ (1621760) 0 0

126 (125-127) 1:6 5 70 (m.p.)

129 (128-130) 1:4 8 60 (m.p.)

93 1:5 6 60 (m.p.)

*oxidation under reflux condition and oxidation at room temperature; Solvent: Hexane aconfirmed by GC, IR and IH NMR; bdetermined by GC analysis; cisolat.ed yield

Table VI - Oxidative* deoximation of aldoximes and ketoximes

Substrate R R Substrate/Oxidant mole ratio Producta Reaction timeb Yieldc (hr) (%)

9a 4-N02-C6H4 H 1:2 lOa 3 89 9b 4-CH)O-C6H4 H 1:2 lOb 3 95

9c C6HsCH=CH H 1:2 10c 3 93

9d C6Hs CH3 1:2 10d 4 94

ge 2-HO-C6H4 H 1:2 lOe 5 73

9r 4-HO-C6H4 H 1:2 lOr 5 84 9g R=R' = -(CH2)s 1:2 109 5 93

9b CH3(CH2)s H 1:2 lOb 5 *under reflux conditions; Solvent: Dichloromethane aconfirmed by GC, IR and IH NMR; bdetermined by TLC analysis cisolated yield 942 INDIAN 1. CHEM., SEC B, MAY 2004

Table VII - Oxidation * of mixture of alcohols with QFC - silica gel

Substrate Substrate/ Products Reaction Yield" Oxidant time" (%) mole ratio (hr)

1- Octanol 1- Octanal 56 + 1:2 + 6 14 2 - Octanol 2 - Octanone

1- Heptanol 1 - Heptanal 29 + 1:2 + 5 66 Benzyl alcohol Benzaldehyde Benzyl alcohol Benzaldehyde 69(49) + 1:2 + 5 19(29) Cyclohexanol Cyclohexanone

*oxidation at room temperature; Solvent: Hexane 'determined by GC analysis; values in parentheses( ) refer to yield obtained under renux condi­ tion

The selectivity of QFC-silica gel in the oxidation of quite stable and effective even after a period of twelve alcohols was ascertained by carrying out the competi­ weeks of its preparation (as indicated by the tive oxidation on a mixture of alcohols. The results consistent yield of benzaldehyde), while QFC, PCC (Table VII) reveal that an aliphatic primary hydroxyl and PFC-alumina tend to lose their effectiveness on group is preferentially oxidised in the presence of an storage. aliphatic secondary hydroxyl group. Further, an aro­ The mechanism of oxidation of alcohols is pro­ matic side chain primary hydroxyl group is oxidised posed based on the foll owing observations (i) The more preferentially than an aliphatic primary hy­ faster oxidation of primary alcohols with an alkyl droxyl group and an alicycli c hydroxyl group. substituent at C-2 carbon such as 2-ethyl-l-hexanol The studies on the stereochemical preference of and neopentyl alcohol than the unsubstituted counter­ QFC-silica gel in the oxidation of cis (11) and trans- parts suggests that there is steric acceleration of rate 4-t-butyl cyclohexanol (12) indicate that the axial hy­ (ii) The faster oxidation of alicyclic alcohols with I droxyl group of the cis isomer (GC; Rt.6.42) is oxi­ strain also supports steric acceleration of rate. This dised faster in high yield than the equatorial hydroxyl implies that the reaction proceeds through a transition group of trans isomer (GC; R t.7.00) (Scheme IV). state in which the strain is relieved. This fact is further The stability and effectiveness of QFC-silica gel supported in the oxidation of 4-r-butyl cyclohexanol was evaluated by carrying out the oxidation of benzyl as discussed previously (ii i) enhancement of the rate alcohol during different periods of storage of the in the oxidation of substituted benzyl alcohols with an reagent. The results were compared with those electron releasing substituent suggests that the oxida­ obtained with QFC, PCC and PFC-alumina. The tion takes place through the formation of chromate results (Table VIII) reveal that QFC-silica gel is ester intermediate (Scheme V).

(CI-h),c~ OFC-Silica gel Ref, 2h, 92% OH 11 (Cl-hbC~ o _O_F_C-_S_ili_ca_ge_I_~/ 13 Ref, 4.5h, 63%

12 Scheme IV- Oxidation of cis (11) and trans-4-t-butyl cyclohexanol (12) RAJKUMAR et at.: QFC-SILICA GEL AS A SELECTIVE. STATIC AND VERSATILE OXIDANT 943

Table VIII - Oxidation * of benzyl alcohol with QFC. QFC - silica gel. PCC and PFC-alumina during storage

Substrate Substratel Storage period Reaction time' Yield' Oxidant weeks (hr) (%) mole ratio

2 91 QFC - Silica gel 1:1.5 4 2 90 6 90 12 87 1 90 2 89 I: 1.5 4 3 85 6 71 12 62 1 90 2 81 1:1.5 4 2 69 6 61 12 54 1 84 PFC-alumina 2 72 1: 1.5 4 3 64 6 52 12 44

•oxidation at room temperature; Solvent: Hexane Isolvent: Dichloromethane 'determined by GC analysis

R' I + R-C-OH ... I H liiiihiiiiiiiiiiiiiiiiii iiiiihiiiiiiiiiiiiiiiiii SG SG 1 , # C=O / R'

i1iiihiiiiiiiiiiiiiiiili iiiiihiiiiiiiiiliiiiiiiiiiiiiiiiiiiiiiiiiiliiiiii SG SG Scheme V-Mechanism of oxidation of secondary alcohol 944 INDIAN 1. CHEM., SEC 8, MAY 2004

Further ESR spectral analysis of the reduced prod­ and OV-l7 packed columns. TLC analyses were per­ uct of the QFC-silica gel showed a single band with a formed on precoated silica gel (silica gel F254 ) plates. g value of 1.982 and this value shows the presence of TLC plates were developed in an iodine chamber 2 d Cr (IV) species. This indicates that a two electron and/or by spraying a solution of 2,4-dinitrophenyl transfer is involved in the oxidation. From these ob­ hydrazine. The surface area of silica ge used was de­ servations the mechanism of oxidation of aicohols is termined using Micromeritics pulse chemisorb. Melt­ proposed to occur through the following steps. (1) ing points of the products were determined on a Raga QFC-silica gel attacks the hydroxyl group to give the hot stage apparatus. chromate ester (2) chromate ester then undergoes cy­ clic hydride transfer to give the carbonyl compound Experimental Section! and the reduced Cr(IV) species as shown in the Preparation of quinolinium tluorochromate mechanism. supported on silica gel. To an ice cold mixture of Thus quinolinium f1uorochromate supported on sil­ Cr(VI) oxide (l5g, 0. 15 mole) and 40% hydrofluoric ica gel on account of its versatility has the following acid (11.3 mL, 0.23 mole), silica gel (45g, 60-120 advantages over the existing supported chromium(VI) mesh; surface area: 253 m2/g) activated at 100°C prior reagents: (a) simple preparation (b) good selectivity to use was added with stirring using a mechanical stir­ (c) prolonged stability (d) substrate/oxidant mole ratio rer. Quinoline (17 .7 mL, 0.15 mole) was then added is minimum (e) work-up of the reaction mixture is dropwise and the resulting yellow orange solid was very simple (f) reaction times are reasonable (g) use­ filtered, washed with water and cold acetone and then ful in the oxidation of acid sensitive substrates (h) dried in vacuum for 2 hr. does not require other complementary techniques General procedillre for the oxidation of alco­ such as microwave ilTadiation or the presence of cata­ hols/oximes. To a stirred slurry of QFC-silica gel in lysts such as Lewis acids?9 No leaching of chromium hexane (approximately 2 mL per gram of the suppOlted species into the reaction mixture. This is very impor­ reagent), a solution of the alcohol in hexane was added tant with respect to the environmental concern. Thus and the reaction mixture was stirred vigorously at room QFC-silica gel is one of the best and least hazardous temperature/reflux condition. The course of the reac­ Cr(VI) reagents and a valuable addition to the existing tion was followed by GC / TLC analysis after every reagents. hour. After completion of the reaction, the reaction mixture was diluted with dry (30-40 mL) Materials and Methods and filtered through a short column of silica gel (2 cm). Alcohols used in the present work were of ex­ The solid residues were thoroughly washed with dry trapure quality (E. Merck, Fluka and Aldrich) and diethyl ether (4 x 20 mL). The combined filtrate on were distilled under reduced pressure/recrystallised evaporation in a rotary evaporator gave the crude prod­ from suitable solvent prior to use. cis and trans uct, which was purified by distillation under reduced t-Butyl were prepared by reported pressure (or) recrystallisation in case of solid products. methods. Oximes were prepared by adopting the stan­ For the oxidative deoximation of oxirnes the above dard procedures. 3D Reagents such as pyridiniulTl procedure was followed in dichloromethane as solvent chlorochromate (PCC)6, quinolinium fluorochro­ under reflux condition. The course of the reaction was mate l3c and pyridinium f1uorochromate supported on followed by TLC analysis (silica gel, pet. ether: ethyl alumina l3c were prepared adopting the reported pro­ acetate 9: I). cedures. The products of oxidation were identified by Oxidation of 1-heptanol (1 d) to 1-heptanal (2d) comparison with authentic samples (IR, GC, IH as a typical exampl,e. QFC-silica gel (8.6 g, 12.5 NMR, b.p. and m.p.). IH NMR spectra were recorded mmole) was made into a slurry with hexane (35 mL) on Bruker DPX-200 (200 MHz) high-resolution FT­ in a two necked RB flask of 100 ml capacity fitted NMR spectrometer using CDCI3 as solvent and with a reflux condenser and a mechanical stirrer. The tetramethylsilane (TMS) as internal standard. IR spec­ solution of I-heptanol (I.l6g, 10 mmole) in hexane tra were recorded in Perkin-Elmer infrared spectro­ (3 mL) was added to the slurry and the mixture was photometer (model: Hitachi 270-50). GC analyses stirred vigorously at room temperature. The course of were performed on Hewlett Packard 5890A gas the reaction was followed by GC analysis (Carbowax chromatograph using flame ionisation detector. The 20M column, Injection temperature: 180°C; Column columns employed in the study were carbo wax 20M temperature: 100°C) after every hour. After comple- RAJKUMA R et al.: QFC-S ILICA GEL AS A SEL ECTIVE, STATIC AND VERSATILE OXIDANT 945 ti on of th e reaction (minimum peri od in which max i­ (b) Dijksman A, Gonza lcz A M , Payeras A M, Arcnds I W C mum conversion was achi eved) the reacti on mi xture E & Shcldon R A, J Alii Chem Soc. 123, 2001 ,6826; (c) Son Y, M akawana V D, Howell A R & Su ib S L, Angell' was stirred for a further peri od of 30 minutes, diluted Chel1l Int Ed Engl, 40, 2001 ,4280: with dry di ethyl eth er (40 mL) and filtered through a (d) M atsuo J, lida D, Ta tani K & Muka iya illa T, 8 1/1/ Ch e/n short column of sili ca gel (2 em). The solid residue Soc Jpn, 75, 2002, 223 . was thoroughl y washed with dry di ethyl ether 2 Cainelli G & Cardi llo G, ChrollliulII uxidations in org(/Ilic chelllistry, Spri nger- Ve rl ag, Bcrl in, 1984. (4 x 20 mL). The combined filtrates on evaporati on 3 Bowcrs A, Hisa ll T G. Jones E R H & Lemi n A J, J Ch elll gave th e crude product, whi ch was di still ed through a Soc, 1953, 2548. short vigereux column to give I-heptanal (b.p. 4 Poos G I. Arih G E, Bcy lcr R E & Sarett L H, J Alii Chelll 62°C13 0 mm Hg) in 83% yield . IR: 2940(w), Soc, 70, 1953, 446. 2850(m), 2710(m), 17 LO (s) and 1470 (m) em-I. 5 Collins J C, Hess W W & Frank F J. Tetrahedron Lell, 1968 , 3363. Oxidation of cholesterol to 5-cholesten-3-one. The 6 Corcy E J & Suggs J W. Te trah edron Lell , 1975,2647. oxidati on was carri ed out with cholesterol (J g, 2.6 7 Bhatac huljec M N. Cha udhuri H S, Da sg upta H S & Roy I mmole) and QFC-sili ca gel (1 0.13 g, 15 mmole) in 35 Synlhesis, 1982.588. mL hexane. The reacti on mi xture was reflu xed and th e 8 Singh J, Ka lsi P S, Jawanda G S & Chahbra B R, ChelllY & In d, 1986,75 1. course of the reacti on was fo ll owed by TLC (sili ca gel; 9 Guzicc F S & Luzz io F A, Synthesis, ] 980,69 1. 10% diethyl ether in hexane). After completi on of th e l Oa) Murugcsa n V & Pa ndu rangan A, Indian J Chelll, 31 B, reacti on the product was isolated by colu mn chroma­ 1992, 377; tography (s ilica gel, 5% dieth yl ether in hexane). 5- b) Abraham Rajkumar G, Ba numathi Arabincloo & Murugc­ cholesten-3-one (m.p. 126 °C) was isolated in 70% sa n V, In dian J Chelll, 39B, 2000, 74 . II (a) McKillop A & Youn g D W, Synthesis. 1979, 40 1 & 481: yield (0.68 g). IR: 2960(s), 1725(s) and 1620(m) em-I; (b) Varm a R S, Green Ch elllistry, 1999, 43 . IH NMR (CDCI}): 8 0.70 (s, 3H), 0.87 (s,3H), 0.93 12 (a) La lancc ttc J M , Rollin G & Dum as P, Can .I Ch elll , 50, (s,3 H), 1.02 (s,3H), 1.02-1.60 (m, 18H), 1.50-2.20 (m, 1972,3058 ; 7H), 2.25 (s, I H), 2.35 (s, I H) and 5.37 (m, IH); Mass: (b) Sa nl ini cllo E, Po nt i F & Manzocch i A, Synthesis. 1978. 534; M/z 384 (M, 56%), 369 (M-C H}, 29%), 27 1 (M-side (c) Singh R P, Subba Rao H N & Sukh Dcv, Tetrahedron. 35. chain ), 229 (55%) and 124 ( 100%). 1979.1 789: Oxidation of citronellol. The reacti on was per­ (e1) Lou J D & Wu Y Y, Synlh CO ll lln l/ n, 17( 14), 1987, 17 17: fo rmed with citronell ol ( 1. 56 g, 10 mmole) and QFC­ (c) LO ll J D & Wu Y Y, Chelliv & IlId, 1987,53 1: (f) Lou J D, Svnth CUIIII/II II I, 19 ( II & 12), ]989, 1841; sili ca gel (1 0.1 4 g, 15 mmo le) in hexane (20 mL). The (g) I-li rano M. Koba yashi T & Morimoto. Synth COllllnllll. reaction mixture was refl uxed and th e course of the 24( 13), 1994, 1823; reaction was fo ll owed by GC analysis (Carbowax (h) Khadi lku r B. Chilnavis A & Kharc A, S)'ntll CUllllnl/n. 20M column; Injecti on temperature: 300°C, Column 26(2). 1996, 205; i) Varma R S & Sain i R K, Tetrahedron temperature: 180°C). T he product was isolated by di s­ Lett, 39, 1998, 148 1. 13 a) Chcng Y S, Liu W L & Chcn S H, Synthesis, 1980,223; til lation under reduced pressure. C it ronell al (b.p. (b) Hcrsov ici J, Egron M & Antonakis, J Chelll Soc Perkin 105 °C/20 mm Hg) was obtained in 88% (1. 37 g) yield. Trans I, 1982, 1967; IR: 2930 (s), 2700 (s), 1700 (s), 1640 (w), 1450 (m) (c) Abraham Rajkumar G, Banumalhi Arabindoo & Murugesan V, Indian J Chelll. 37B, 1998,596; and 1375 (m) em-I; IH NMR (CDCl ): 8 0.98 (d, 3H), 3 (d) Abraham Rajkllmar G. 13anumalhi Arabindoo & Murugcsan 1.08-1 .47 (m, 3H), 1. 6 1 (s, 3H), 1.70 (s, 3H), 2.03(m, V, Synlh CUllllnl/lI. 29( 12). 1999, 2 105. 2H), 2.36 (dd, 2H), 5. 10 (t, IH) and 9.78 (s, IH). 14 (a) Frcc hct J M J. Wa rn ock J & Fara ll M J• .1 Org Chelil. 43. 1978,26 18; Acknowledgement (b) Frcc hcl J M J. Darling P & Farall M J, J Org Chell/. 46 . This research was supported by University Grants 1981 , 1728; (c) Abraham S, Rajan P K & Srcck umar K. Proc Indian Acad Commission (UGC), New Delhi . G A Rajkumar Sci, 108(5), 1996. 437; thanks CSIR, New Delhi fo r the award of Seni or (d) Abraham S, Rajan P K & Srcckulllar K, Illdiall J Che/II , Research Fell owship. The authors are grateful to 3713, 1997.769. Prof. K K Balasubramani an, liT , Chennai, fo r th e 15 Ba logh V. FClizoll M & Golricr M , J Org Chelll, 36, 1976. 1339 . valuble suggestions. 16 Cboucla ry 13 M. Lakshmi Ka nl<1m M. Rahman A. VCnKal Reddy eh & Kotccswa ra Rao K. Allgew Chelll 1111 Ed Ell gi. References 40. 200 I. 763 . I For re cent work scc u) TohnlJ H, Takizawa S, Maegawa T & 17 Brown 1-1 C, Flctchcr MRS & Johan nesa n R B. J 1\111 Ch elll Kita Y, Angell' Chelll Int Ed Engl. 39, 2000, 1306: Soc. 73, 1951. 2 12. 946 INDI AN J. CHEM .. SEC B, MA Y 2004

18 Pa ri sh E J. Honda H, Chitrakorn S & Li va nt P, Lipids, 26, 1978, 212. 1991,675. 25 Drabow icz J, Sy" th esis, 1980, 125. 19 Firo uzabadi H, Vessal B & Naderi M, Tetrahedrall Lell, 23, 26 Jad hav V K, Wadgao nk ar P P, Jos hi P L & Sa lun khe M M. 1982, 1847 . SYllth Co III II I 1111 , 29( II ), 1999, 1989. 20 Firouzabadi H & Sarda ri an A, SYllth COII IIIIIIII , 13, 1983, 863. 27 Tangestanin ejad S, Hab ibi M H & Iravani M R, J Ch elll Res 21 Kl obb M T, A COlllprehensive Treatise 0 11 Ill orgall ic ([ lid (S), 1998,456. Th eoretical Chelllistry, Vo l XII , Longmans. London, 1965. 28 Zhang G S, Yang D & Chen M, Org Prep Proc lilt, 30, 1998. 22 Firouzabadi H, Nade ri M, Sard ari an A & Vessal B, SYllth 7 13. CO IIIIIIUlI , 13, 1983, 6 11 . 29 l\1 oham madpoor Ba ltork I, Sadeghi M M & Ad ibi A, Mole­ 23 Walke r F A, Sigel H & McCormic k, Illorg Chelll , II , 1972, cliles, 6, 2001 , 900. 2756. 30 Vog el's text book of practical orgallic chelll istry, Longman 24 Ma loney J R, Lyle R E, Saaved ra J E & Lyle G G, SYllth esis, Scient ific and Technical, England.