INDIAN J. CHEM., VOL. 17A, JANUARY 1979

TABLE 2- EFFECT OF VARYINGACIDITYON ZERO ORDERRATE CONSTANTIN THE OXIDATIONOF KETONES

[Solvent = 50% HOAc (v/v); substrate conc. = 0'04M;TI(III) conc.= 0'005M; temp.= 60°]

Substrate 104~o (mol litre-! min-i) in

[H2S04], M: 0·5 1'0 1'5 2'0

Acetophenone 0·23 0·74 1·73 3·25p-CH.-acetophenone 0·40 1-33 2·66 4'43p-Cl-acetophenone 0·19 0'48 1'25 1·90p-Br-acetophenone 0·19 0'52 0·94 1'86p- N02-acetophenone 0'08 0'26 0'52 0'93

[H2S0.],M: 0·25 0'5 0·75 1'0

Acetone 0·38 1'06 1-65 2·65Ethyl methyl ketone 5·52 11'21 15·48 20'65n-Propyl methyl 4-10 7'47 14'86 18·35

ketoneIsobutyl methyl 2·04 3-61 4·69 7'25

ketoneHexanone" 11·31 20'62 29·41Octanone= 4·38 7'78 14-10Pentanone= 2·45 4·29 9·40Heptanone= 1'88 3-17 4'70 5'65

*[Substrate] = O'OlM; [Tl(III)] = 0·0045M.

TABLE 3 - SOLVENTEFFECT IN THE OXIDATIONOFKETONESBY TI(III)

[Substrate cone. = 0'04M; Tl(III) = 0'005M; H2SO. cone.= 0·5M; temp = 60°]

10'ko (mol litre-i min-i)Water:HOAc Acetone Aceto- P-CH3- p-Cl- p-Br p-NO~

phenone aceto- aceto- aceto- aceto-phenone phenone phenone phenone

0'83 0'25 0·30 0·140·60 0·21 0'24 0·120·40 0'19 0·19 0·100·52 0·16 0·16 0·080'81 0·30 0·30 0'151·35 0·69 0'66 0'354'96 2·87 2'73 1·659·60 7'75 6·72 4'20

70: 3060: 4050: 5040: 6030: 7020: 8010: 90

5: 9S

1·501'211'061·321·622'435'74

11·86

0'430·370·230·260'561·051'962'81

ethyl methyl ketone> n-propyl methyl ketone> iso-butyl methyl ketone> acetone. The order of reacti-vity is in consonance with the stability of enols.

The order of reactivity in the case of cyclic ketones iscyclohexanone > cyclooctanone > cyclopentanone >cycloheptanone. The higher reactivity of cyclohexa-none is a natural consequence of higher enolic content.

The enolization of ketone consists of two steps:(i) equilibrium protonation of carbonyl group; and(ii) deprotonation of cc-carbon of the conjugate acid.These two steps affect the rate of enolization depend-ing on the structural factors. The P-value obtainedfor acetophenones is -0·3 indicating that both steps(i) and (ii) are controlling the rate of enolization.

The reaction rate is retarded with increase in aceticacid till about 60% acetic acid and then increases withincreasing proportion of acetic acid (Table 3).

It appears that the equilibriumTI(OAc)3+H+~T1(OAc)2+HOAc

is favoured till about 60% acetic acid is reachedand due to this competing equilibrium rate ofenolization in the presence of acid of the substrate

98

I

+o OH

" fast "R-CHs-C-R' + H+.= R-CH2-C-R'

+OH OH"slow I

R-CHs-C-R' --+ R-CH = C-R' + H+OHI· fast

R - CH = C - R' + Tl(III) (OAc). __ -+0+

IR - CH = C - R' + TlI(OAc) + HOAc + -OAc

0+ 0~ I + II -QAc

R-CH = C-R' _-+- R-CH-C-R' ---+OAc 0 fast

I "R-CH-C-R'

Scheme 1

is hindered thus causing an overall retardation inthe rate. After this optimum percentage of aceticacid is reached the reverse equilibrium is favouredwhich leads to higher rate of enolization causing anacceleration in the rate. This is a first instance ofdual solvent effect observed in Tl(III) oxidation so far.

It is clear from the results that the mechanisminvolves rate determining enolization of the ketones.Further, the plot of log ko (oxidation of ketonesby lead tetraacetate) versus log ko [TI(III) oxidationof ketones] is linear, indicating identical mechanismin both the processes, further confirming that therate of enolization is the predominant step in boththe oxidations.

In general, TI(III) functions as a two-electronoxidant and so Tl(III) reacts with the enol of theketone to give the intermediate oxonium ion whichis mesomeric with carbonium ion in a two-electrontransfer fast step which finally yields the acetoxyderivative also in a fast step (Scheme 1).

One of the authors (S.N.P.) is grateful to the CSIR,New Delhi, for the award of a juniorresearch fellowship.References

1. LITTLER,J. S., J. chem, s«., (1962), 827.2. RADHAKRISHNAMURTI,P. S. & PATI, S. N., Indian J.

Chem., 16A (1978), 319.3. RADHAKRISHNAMURTI,P. S. & PATI, S. N., Indian J.

Chem., 16A (1978), 139.4. WIBERG,K. B. & EVAN,R. J., J. Am. chem . Soc., 80 (1958),

3019.5. HENRY, P. M., J. Am. chem. s»; (1966), 1597.

Some New Adducts of Oxo OrganotinfI'V)Compounds

SURA] PRAKASHNARULA* & RAMESHKUMARSHARMADepartment of Chemistry, Panjab University

Chandigarh 160014

Received 12 January 1978; accepted 20 June 1978

1 : 1 and 1: 2 addition compounds of titanium(IV)chloride with u-oxo-btsjtrfphenyltlnffvjj ; of ethyltin(IV) and diethyltin(IV) Chlorides with l1-oxo-bis [tr l-rr-butyltin(IV)] ; 1 : 1 adducts of antimony(V) chlortde with

r

p-oxo-bis [triphenyltin(IV)] as well as 1 : 1 adducts oftitanium(IV), tin(IV) and antimony(V) chlorides withdi-rr-butyltin oxide have been isolated. The structuresof these compounds have been elucidated on thebasis of elemental analyses and infrared spectralstudies.

IN continuation of our studies on oxo organotin(IV)compoundsv'' we report here the synthesis and

characterization of some new adducts of oxo orga-notin(IV) compounds.

[L-Oxo-bis[triphenyltin(IV)], [L-oxo-bis[tri-n-butyl-tin(IV)] and di-n-butyltin oxide supplied by MisAkzo Chemicals Ltd, Kirby (UK) were used assuch. Tin(IV) , titanium(IV) and antimony (V)chlorides (Riedel, pure) were distilled before use.Ethyltin(IV) and diethyltin(IV) chlorides were pre-pared as reported".

Adducts (1: 1 and 1: 2) of u-oxo-bisjtriphenyltin(IV)] and [L-oxo-bis[tri-n-butyltin(IV)] were obtainedby essentially the same procedure as reported earlier".However, for the preparation of 1: 1 ad ducts ofdi-n-butvltin oxide, the oxide was taken as a sus-pension "in dry carbon tetrachloride and the Lewisacids (slight excess), in the same solvent were addedin the manner described before'. The productsobtained were washed, dried and analysed. Allthe relevant physical and analytical data are recordedin Table 1.

Infrared spectra of. the complexes were recordedin nujol on a Perkin-Elmer spectrophotometer model621 using caesium iodide optics. The region wherenujol absorbs, was checked either using potassiumbromide pellets or fiuorolube mull.

TABLE 1- PHYSICAL AND ANALYTICAL DATA OF THECOMPLEXES OF WOXO-BIS[TRIORGANOTIN(IV)] AND DI-n-

BUTYLTIN OXIDE

Compound Colour and state Found (Calc.)(yield, %) %

-------Tin Chlo-

rine

TiCI•.A White powder 26'25* 15·62(82) (26'10) (15'71)

TiCI•.2A Brown powder 29·51* 8'60(81) (29'16) (8'77)

SbCIs·A Brown crystalline solid 23'09* 16·98(84) (23'29) (17'52)

EtSnCI3·B White powder 41·77 12·90(85) (42'10) (12·57)

Et2SnCI2·B White fluffy powder 41·70 8'20(70) (42·09) (8'44)

EtSnCI3·2B White powder 40'40 7·20(74) (40'49) (7040)

Et2SnCI2·2B White fluffy powder 40·87 4'26(62) (41-10) (4'95)

SnCI•.C White crystalline solid 40'10 27'60(90) (46'45) (27'95)

'fiCI•.C White crystalline solid 26'48* 32·18(92) (26'94) (32-42)

r;bCls'C Grey crystalline solid 21·42* 32'25(94) (21,57) (32-45)

*Tin was estimated from mixed oxides.. A = Woxo-bis[triphenyltin(IV)]; B = Woxo-bis[tri-n-butyl-

tm(IV)]; and C = di-n-butyltin oxide.

I

NOTES

The adducts isolated in the present study aresolids which decompose on heating and these cannot be sublimed even under vacuum (--..0·2 mm).Due to extreme insolubility of the compounds incommon organic solvents, their molecular weightsand molar conductances could not be determined.

vasSn-O-Sn absorption in [L-oxo-bis[triphenyltin(IV)] and [L-oxo-bis[tri-n-butyltinlIV)] is known tooccur at 775 and 783 (IR bands in cm-l) respec-tively+", These frequencies suffer a negative shiftof the order of 40-69 on complex formation. Theshift is slightly lower in 1: 2 complexes as comparedto that in 1: 1 complexes, which is expected-. Acomparison of these absorptions in ethyltin(IV)and diethyltin(IV) chloride complexes of [L-oxo-bis[tri-n-butyltin(IV)J with that of tin (IV) chloridecomplex of the same base, reveals that vasSn-O-Snabsorptions appear at lower frequencies in thelatter easel. This may be due to the weak acidstrength of the alkyltin(IV) chlorides", vO~Mbands are known to occur between 387 and 466 inthe oxy-cornplexes of tin (IV) and alkyltin(IV) chlo-rides while the complexes of titanium(IV) andantimonyfV) chlorides give these absorptions inthe regions 440-555 and 390-440 respectively=".The new bands between 392 and 471 may be assignedto stretching modes of O-M bonds in these com-plexes. However, relatively higher frequencies ofsuch bands in 1: 2 complexes may be due to differentstereochemistries of the two types of adducts.vM-Cl frequencies in the oxy complexes of the acidsused here are known to occur between 203 and3807-1°. The existence of bands between 295 and342 for 1: 1 adducts and between 308 and 352 for1 : 2 complexes are in fair agreement with bandpositions of five and six coordinate complexes ofthe metal chlorides+w. vaSSnC3 and vaSSnC3 fre-quencies occurring at 598 and 511 in Woxo-bis[tri-n-butyltin(IV)J shift to 565-75 and 506 on complexformation. Vas SnPh3 mode of [L-oxo-bis[triphenyl-tin(IV)J remains almost unaltered on complexa-tion.

Harda-' has isolated adducts of Woxo-bis[tri-methyltin(IV)] with trimethyltin(IV) bromide andiodide and has suggested them to be oxonium salts.Kriegsmann et al,12 have confirmed the structureof these compounds on the basis of infrared andRaman spectroscopy. On comparing the infraredspectral data of the oxonium salts-" and of thead ducts , it is observed that there is insignificantchange in Vas Sn-O-Sn frequency in the former casewhereas it suffers appreciable negative shift in thepresent complexes. Moreover, even after takinginto consideration the nature of organic groupsattached to tin atom in the two reacting species,there are appreciable differences in the absorptionvalues. A similar disagreement has also beenobserved in the IR data of the present 1: 2 adductsand 1: 2 ionic adducts reported in literature13,14.

Thus the compounds obtained here may be con-sidered as non-ionic in nature. On the other hand,there is a reasonable agreement between the vO~Mand vM-Cl absorptions of these complexes andthose of other molecular oxy adducts of the Lewisacids studied-". Hence the reactions may be re-presented as shown in Eqs. 1 and 2.

99

\

INDIAN J. CHEM., VOL, 17A, JANUARY 1979

(RsSn)z 0: + MCln ~ (R3Sn)2 0: ~ MCln

2(RsSnh 0: + MCln~[(R3Sn)2 0:]2 MCln

where R = n-C.Hg or C.H.,M = Sb, Ti, EtSn or ~t2Sn andn = 5, 4, 3 or 2.

Di-a-butyltin oxide is known to be a polymericcompound with alternate Sn-O-+Sn bonds [Vas

Sn-O-Sn at 564 (ref. 16)], thus rendering thetin atom penta-coordinated'". It has been observedthat Vas Sn-O-+Sn band suffers negative spectralshift of the order of 14-29 on adduct formation.The presence of new bands between 380 and 470is suggestive of the existence of O-+M bonds in theadducts=". vM-Cl absorptions have also beenidentified between 295 and 345 which is withinthe range for oxy complexes of these acids7-1o•

Vas SnC2 frequency shifts to 570 in the adduct oftin(IV) chloride. However, with other Lewis acidsused, these absorptions could not be identified withcertainty. On the basis of analytical and spectraldata, the structure of these ad ducts may berepresented as:

l C.H. ~- --~n--?--C4H. MCln x

where n = 4 or 5 and M = Sn, Ti or Sb

Authors are grateful to Akzo Chemicals Ltd,Kirby (UK), for gift samples of organotin oxides.One of the authors (R.K.S.) is grateful to CSIR,New Delhi, for financial assistance.

References

1. PAUL, R. C., MAHAJAN,V. K., AHLUWALIA,S. C., SHARMA,R. K. & NARULA, S. P., Inorg. nuci. chem, Lett., 9(1973), 893.

2. PAUL, R. C., SHARMA, R. K., WALIA, R. & NARULA,S. P., Indian j. Chem., 16A (1978), 544.

3. LUIJTEN, J. G. A. & VAN DER KERK, G. J. M., Investi-gations in the field of organotin chemistry (Tin ResearchInstitute, London), 1959, 157.

4. KRIEGSMANN, H., HOFFMANN, H. & GEISSLER, H., Z.anorg, allg, Chem., 341 (1965), 24.

5. KRIEGSMANN,H. & GEISSLER, H., Z. anorg, allg. Chem.,323 (1963), 170.

6. STROHMAER,W. & MILTERBERGER,K., Z. phys. Chem.,(N.F.), 17 (1958), 274.

7. TANAKA,T. & KAMITANI, T., Inorg. chim, Acta, 2 (1968),175.

8. PAUL, R. C. & CHADHA,S. L., j. inorg, nucl, Chem., 31(1969), 2753.

9. PAUL, R. C., MADAN,H. & CHADHA,S. L., j. inorg, nucl.Chem., 36 (1974), 737.

10. NAKAMOTO, K., Infrared spectra of inorganic and co-ordination compound (John Wiley, New York), 1963,118.

11. HARDA, T., Bull. chem, Soc. japan, 15 (1940), 455.12. KRIEGSMANN,H. & HOFFMANN,H., Z. anorg. allg. cu-«,

321 (1963), 224.13. CLARK, H. C. & O'BRIEN, R. J., Inorg. cu«; 2 (1963),

740.14. KUMAR DAs, V. G. & KITCHING, W., j. organometal,

Chem., 10 (1967), 59.15. BRUNE, H. A. & ZEIL, W., Z. phys. cu«. (N.F.), 32

(1962), 384.16. CUMMINS,R. A., Aust. j. Chem., 18 (1965), 98.17. GOL'DANSKII, V. 1., MAKAROV,E. F., STUKAN, R. A.,

TRUKHTANOV,V. A. & KHARPOV, V. V., Dokl. Akad.Nauk; SSSR, 151 (1963), 357.

100

I

... (1)

... (2)

Nuclear Magnetic Resonance Study of 59COin Some Co(III) Complexes

S. S. DODWAD* & M. G. DATARtPhysical Chemistry Laboratory, Institute of Science

Bombay 400032

Received 19 january 1978; revised 20 April 1978;accepted 20 May 1978

From the NMR spectra of S9CO,in Co(III) complexesof the type [Coen2(R)CI]Cl2where en = ethylenediamineand R = dicyandiamide or an aromatic amine, thechemical shift values (a) have been determined. Thea values have been calculated theoretically also ustngGriffith and Orgel's formula. The observed and cal-culated a values agree well. Taking a values as a mea-sure of ligand field strength a decreasing order of ligandfield strengths in terms of amine R is reported.

MAGNETIC susceptibilities and temperature-independent paramagnetism (Li.p.), Xp, values

of the Co(III) complexes of the type [Coen2(R)CI]CI2where R = dicyandiamide or an aromatic aminehave been reported by us-. On the basis of thetheory of Griffith and Orgel-, we have also cal-culated the Xp (t.i.p.) values theoretically". In thepresent investigation 59CO NMR spectra of thecomplexes have been recorded. From the spectra,the chemical shift values (cr) have been determinedand compared with those calculated using Griffithand Orgel's formula.

Concentrated aqueous solutions of the complexeswere placed in the probe of the Varian wide-linespectrometer, V-4200 which was coupled with a12 inch electromagnet. Solution of Co(en)aCla wasused as an external standard. The stabilities ofRF oscillator and the magnetic field were of theorder of 1 in 105. The apparatus could give aresolution of about 50 milligauss. The NMR forCo(en)aCla and the complex under examinationwere recorded by scanning the field over a limitedrange of 7000 gauss. Values of cr% were calculatedfrom the separation between the two lines in thespectra of Co(en)aCla and [Co(en)2(R)CI]CI2.

From these cr% values the cr% values relativeto KaCo(CN)6 were calculated (Table 1). UsingGriffith and Orgel's formula, cr% values were cal-culated theoretically also. The energy of separation(~E) values required for this purpose have also beenreported in the same table.

An examination of the results shows that theobserved values are negative. This is because theresonance occurs at a field lower than that forKaCo(CN)6' Further, it is seen that the calculatedvalues are lower than the observed ones. Griffithand Orgel estimated the probable errors in theircalculation of a and came to the conclusion that thetheoretical calculation can at best give an agreementwithin 20% of the observed data. Kanekar andNipankar- and Datar and Patankar- have also madesimilar observations.

The results obtained in the present investigationare within ± 20% of the calculated values and

+Present address: Rajaram College, Kolhapur, Maha-rashtra.