IDdhlD Journal of Chemistry Vol. 16A, April 1978. pp. 337-339 Studies on Insertion Reactions of Carbon Disulphide, Phenyl & p-Bromophenyl Isothiocyanates & Phenyl Isocyanate Across Tin-Nitrogen Bond S. N. BHATTACHARYA* & PREM RAJ Department of Chemistry, University of Lucknow, Lucknow 226007 Received 14 June 1977; revised 17 October 1977; accepted 5 November 1977 Insertion reactions of unsaturated substrates, viz. carbon disulphide, phenyl and p- ~rom~phenyl isothiocyanate and phenyl isocyanate across the tin-nitrogen bond of trtorgano- tin aztdes, R 3 SnN. (R = n-butyl, cyclohexyl, benzyl, phenyl and p-tolyl) have been studied. The products have been characterized by IR and UV spectra and elemental analyses. The contrast- ing behaviour of carbon disulphide towards trialkyl- and triaryl-tin azides and the possible mechanism for such reactions have also been discussed. T HE addition rec ctic ns of r nsaturated substrates (X= Y) to a wide variety of organotin mole- cules ha ve been reported. These rec ctior.s in general may be represented by Eq. (1) :7Sn-A+X = Y ~:7 Sn-X- Y -A (1) where A = Nl-6, 0 7 ,8, C9,10, Hll,12 and (X= Y) an unsaturated substrate, S=C=S, O=C=O, Ph- -N =C=S, Ph-N =C=O, S02' S03' C=C and C=c. Among such rea cticns of orgc r.otin molecules containing Sn-N linkages, La ppert-" has exten- sively studied triorganostannyl amines (R 3 Sn)xNRg_ x while Kupchik=" and coworkers have investigated similar reactior.s with triorganostanr.yl cyar.amides, RaSnNHCN and carbodiimides, (RaSn)2N2C. Tri- organotin azides. RaSnNa which contain direct tin- nitro~en bond are also expected to undergo similar reactions. Recently Dunn and Oldfield-" briefly ex~ mined some insertion rea ctions of triorganotin a zides, RaSnN3 (R = Bu, Ph) with phenyl isothio- cyanate and also followed a reaction between B\laSnN3 and carbon disulphide by UV spectra without isola ting the rea ction products. In continuation of our studies on Sn-N bonded organotin pseudoha lidesw+? we now report the reactions of triorganotin azides, R a SnN 3 (R = n-Bu, cyclohexyl, benzyl, phenyl and p-tolyl) with the ~nsatUTated substrates, viz, carbon disulphide, phenyl Isocyanate, and phenyl and p-bromophenyl isothio- cyana tes, Materials and Methods !riorganotin azides2.l7.l8 and p-bromophenyl iso- thiocyanatet? were prepared by reported procedures. Phenyl isothiocyanate and phenyl isocyanate of AR grade were used as such. Carbon disulphide was dried over molecular sieves and distilled before use. The infrared spectra (v ma " in crrr+) were recorded on a Perkin-Elmer 177 gra ting spectrophotometer. ·To whom correspondence should be addressed. UV absorption spectra were recorded with a Perkin- Ehn~r 202 spectrophotometer using 1 em quartz cell In cyclohexane. All manipulations were carried out in dry nitrogen atmosphere. Two represer.ta tive insertion reactions of the triorgrnctin ezides with the unsaturated substrates a re described below. Further details are given in Table 1. Reaction of (cyclohexylhSnN3 with carbon di- sulphi~e-Tri-cyclohexyltin azide (1·02 s. 0·0025 mole) 111 ether (40 ml) W2 s refluxed with four-fold excess of carbon disulphide (0·76 g, 0·01 mole) for 4 hr. filtered and then concentrated to yield tri- cyclohexyltin isothiocyana te, m.p. 120° (lit. 20 m.p. 121 0), ~ie~d 0·4 g (37%); IR: 2070 (vas N =C=S). III similar experiments triaryltin azides (Ar = C6HS or p-C6HaC6H4) were recovered quantitatively even after 8 hr refluxing. Reaction of (phenyl)aSnNa with phenyl isothio- c:yanat~- In a representative experiment triphenyl- t111 azide (1'96 g, 0·005 mole) and phenyl isothio- Cy<1n8 te (0·67 g, 0·005 mole) were stirred together at 140 0 for 3 hr. The resulting brown residue was extracted with boiling hexane and on cooling, the extract ga ve white crystals of l-phenyl-f-Itriphenyl- stannyljtetrazole-Svthione (0·8 g. 31 %). m.p. 134° (Found: C, 57·20; H, 3·74; N, 10'42; Sn, 22·72. Calc. for C2sH20N4SSn: C, 56·97; H, 3·79; N, 10·62; Sn, 22·52%. Results and Discussion l!-eaction~ with R'-N=C=X (X = S or 0)- Tnorgal}-otm. azides react with phenyl and p-bromo- phenyl isothiocyana tes to yield l-phenyl- or 1-p-bro- mal?h~nyl. -4-(triorganostannyl)tetra zole-S-thione (I). Similarly, pher.yl isocyanate gave 1-phenvl-4-(tri- organ~stannyl)tetrazoliLone, contrary to the ob- servatJ?n of D~nn and 0ldfield 13 , who reported the formation of diphenylurea in this reaction. The melting points of the reaction products r~ma.ined unchanged even after repeated recrystal- Iization from appropriate organic solvent and thus, 337
Transcript
IDdhlD Journal of ChemistryVol. 16A, April 1978. pp. 337-339
Studies on Insertion Reactions of Carbon Disulphide, Phenyl &p-Bromophenyl Isothiocyanates & Phenyl Isocyanate
Across Tin-Nitrogen BondS. N. BHATTACHARYA* & PREM RAJ
Department of Chemistry, University of Lucknow, Lucknow 226007
Received 14 June 1977; revised 17 October 1977; accepted 5 November 1977
Insertion reactions of unsaturated substrates, viz. carbon disulphide, phenyl and p-~rom~phenyl isothiocyanate and phenyl isocyanate across the tin-nitrogen bond of trtorgano-tin aztdes, R3SnN. (R = n-butyl, cyclohexyl, benzyl, phenyl and p-tolyl) have been studied. Theproducts have been characterized by IR and UV spectra and elemental analyses. The contrast-ing behaviour of carbon disulphide towards trialkyl- and triaryl-tin azides and the possiblemechanism for such reactions have also been discussed.
THE addition rec ctic ns of r nsaturated substrates(X= Y) to a wide variety of organotin mole-cules ha ve been reported. These rec ctior.s
in general may be represented by Eq. (1):7Sn-A+X = Y ~:7 Sn-X- Y -A (1)where A = Nl-6, 07,8, C9,10, Hll,12 and (X= Y)an unsaturated substrate, S=C=S, O=C=O, Ph--N =C=S, Ph-N =C=O, S02' S03' C=C andC=c.
Among such rea cticns of orgc r.otin moleculescontaining Sn-N linkages, La ppert-" has exten-sively studied triorganostannyl amines (R3Sn)xNRg_xwhile Kupchik=" and coworkers have investigatedsimilar reactior.s with triorganostanr.yl cyar.amides,RaSnNHCN and carbodiimides, (RaSn)2N2C. Tri-organotin azides. RaSnNa which contain direct tin-nitro~en bond are also expected to undergo similarreactions. Recently Dunn and Oldfield-" brieflyex~ mined some insertion rea ctions of triorganotina zides, RaSnN3 (R = Bu, Ph) with phenyl isothio-cyanate and also followed a reaction betweenB\laSnN3 and carbon disulphide by UV spectrawithout isola ting the rea ction products.
In continuation of our studies on Sn-N bondedorganotin pseudoha lidesw+? we now report thereactions of triorganotin azides, RaSnN3 (R = n-Bu,cyclohexyl, benzyl, phenyl and p-tolyl) with the~nsatUTated substrates, viz, carbon disulphide, phenylIsocyanate, and phenyl and p-bromophenyl isothio-cyana tes,
Materials and Methods!riorganotin azides2.l7.l8 and p-bromophenyl iso-
thiocyanatet? were prepared by reported procedures.Phenyl isothiocyanate and phenyl isocyanate ofAR grade were used as such. Carbon disulphidewas dried over molecular sieves and distilled beforeuse.
The infrared spectra (vma" in crrr+) were recordedon a Perkin-Elmer 177 gra ting spectrophotometer.
·To whom correspondence should be addressed.
UV absorption spectra were recorded with a Perkin-Ehn~r 202 spectrophotometer using 1 em quartzcell In cyclohexane. All manipulations were carriedout in dry nitrogen atmosphere.
Two represer.ta tive insertion reactions of thetriorgrnctin ezides with the unsaturated substratesa re described below. Further details are given inTable 1.
Reaction of (cyclohexylhSnN3 with carbon di-sulphi~e-Tri-cyclohexyltin azide (1·02 s. 0·0025mole) 111 ether (40 ml) W2 s refluxed with four-foldexcess of carbon disulphide (0·76 g, 0·01 mole) for4 hr. filtered and then concentrated to yield tri-cyclohexyltin isothiocyana te, m.p. 120° (lit.20 m.p.1210), ~ie~d 0·4 g (37%); IR: 2070 (vas N =C=S).
III similar experiments triaryltin azides (Ar =C6HS or p-C6HaC6H4) were recovered quantitativelyeven after 8 hr refluxing.
Reaction of (phenyl)aSnNa with phenyl isothio-c:yanat~- In a representative experiment triphenyl-t111 azide (1'96 g, 0·005 mole) and phenyl isothio-Cy<1n8te (0·67 g, 0·005 mole) were stirred togetherat 1400 for 3 hr. The resulting brown residue wasextracted with boiling hexane and on cooling, theextract ga ve white crystals of l-phenyl-f-Itriphenyl-stannyljtetrazole-Svthione (0·8 g. 31%). m.p. 134°(Found: C, 57·20; H, 3·74; N, 10'42; Sn, 22·72.Calc. for C2sH20N4SSn: C, 56·97; H, 3·79; N, 10·62;Sn, 22·52%.
Results and Discussion
l!-eaction~ with R'-N=C=X (X = S or 0)-Tnorgal}-otm. azides react with phenyl and p-bromo-phenyl isothiocyana tes to yield l-phenyl- or 1-p-bro-mal?h~nyl. -4-(triorganostannyl)tetra zole-S-thione (I).
Similarly, pher.yl isocyanate gave 1-phenvl-4-(tri-organ~stannyl)tetrazoliLone, contrary to the ob-servatJ?n of D~nn and 0ldfield13, who reported theformation of diphenylurea in this reaction.
The melting points of the reaction productsr~ma.ined unchanged even after repeated recrystal-Iization from appropriate organic solvent and thus,
337
INDIAN J. CHEM., VOL. 16A, APRIL 1978
TABLE1 - REACTIONSOIf UNSATURATEDSUBSTRATES(X= Y) WITH TRIORGANOTIN AZlDES (RaSnNs)
R.SnN. Unsatu- Molar Reaction(a) Product Yield m.p. Mol. formula Found (Calc.)(R=) rated ratio period (hr) (%) (0C) %
(a) Reactions without solvent except in the case of carbon disulphide.(b) b.p. 144-46°/2 mm (lit. II b.p. 146°/2 mm).
excluded the possibility of the products beingmixture of the reactants. The spectroscopic datasupported the forma tion of the cyclic products (I)<' s is evident by the absence of vasNa ",2080(ref. 17). The vasNa is very strong and suffersnegligible shift by the environmental groups. Itsabsence, therefore, is a guarantee the t the com-pounds are free of this structural entity. Theproducts formed with aryl isothiocyanates endcyana tes exhibit a band of va ria ble inter-sity in theregion 1305-1225 which in the absence of VasN3
has been assigned to the cyclic -N -N =N linkage'".The VasN3h-s also been reported to appearZ2.23 inthe region 1340-1175. However, Lieber et al:U h.ave,from a study of a series of tetra zole derivatives,assigned the band in the region 1300-1270 to thecyclic -N -N =N - linkage, The formation of t~ecyclic product is further confirmed by the dIS-appearance of N =C=S or N =C=O absorptionbands from Ph-N=C=S or Ph-N=C=O around2080± 5 (ref. 14) or 2275 (ref. 15) respecti~el~iand the appearance of a new bard in the regroi.1395-1310 due to exocyclic C=S and a band in thecarbonyl region25 around 1700. The appearance ofa weak band in the region 1100-1000 has been
338
assigned to skeletal vibrations of the tetrazolering28. The UV absorption spectra of I exhibit acharacteristic prominent maxima in the region of260-290 nm similar to that exhibited by I-phenyl-tetrazole-5-thiol derivo tivesw (;"max 276 nm).
Reaction with carbon disutphide - The reactionsof CS2 are confined only to the trialkyltin azides(Eq. 2) yielding the corresponding isothiocyanates.
S =C=S+ (Alk)3SnN3-+ (Alk)aSnNCS + N,+S ... (2)The formation of triorganotin isothiocyanates canreadily be followed by the disappearance of asharp band around 2080 che r.cteristic of the azidogroup-? and the appearance of a relatively broadband shifted towards the lower frequercy by about30-40 crrr".
Mechanism - The most probable mechanism forsuch reactions cen be considered rs 1,2-dipolaraddition to the unsatura ted substra te -IN =2C=X orIS=2C=IS or in view of the conjugated unsaturatednature of the azido group ·_IN =2N =3N -<'s 1,3-addition to the triorgar.otin azide through theformation of the cyclic intermediates (I) and (II).
The intermediate (II) is uLstable18 and breaksdown along the dotted lines shown in II to give
BHATTACHARYA & RAJ: INSERTION REACTION ACROSS Sn-N BOND
I
S=C=S StC=S~ " ~-J-t. I ----. RJSnNCStN2+SN=N=N-SnR3 N \N-SnR3\\ 'IN\
(II)'
RsS'1NCS, N2 ar.d S. The evidence for such amode of decomposition has e8 rlier been reported-".
It has been concluded that essent irI characteristicof the unsa tura ted substrr tes is that it should besusceptible to a ttack by nucleophiles-. Therefore,the ideal reactions are the ones in which theunsaturated substrate contains electron withdrawinggroups and the azido group containing moleculeshave electron relecsir.g ter.der.cy. It ma y be notedthat acetonitrile, CHsCN is not an effective dipoleunless assisted by strong electron withdn. wir:ggroups, e.g. CCIsCN is quite effective dipole='. Thefailure of the re: ctic ns of carbon disulphide andtriaryltin c zides may partly be then due to theelectron with dr. wing effect of the phenyl rings sincealkyltin compounds rei: ct rea dily. Substitution ofa -CH2 group between tin and the phenyl ringas in tribenzyltin a zide, also makes the reactionpossible. Different courses of reactioi s followed bytrialkyl-and triaryl-tin ozides based on their relativeLewis acidity have a lso been previously reported''.Further, in view of the svmmetricaI fa ture of theS=C=S, which is a lso a weak dipole, the formationof the intermediate (II) does not take ph ce rei dily.Cr.rbon dioxide (O=C=O) under identical cor.ditioi shr s also been fonr.d to be ineffective ever: tow; rdstributyltin . zide'",
AcknowledgementOne of the authors (P.R.) is grdeful to the
CSIR, New Delhi, for the <: ward of a post-doctoralfellowship.
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