1972 2793Constitution of the Adducts derived from Tertiary Phosphine Oxides andArenesulphonamidesBy David W. Allen, Department of Chemistry, Sheffield Polytechnic, Pond Street, Sheffield S1 1 WBFrederick G. Mann.' University Chemical Laboratory, Lensfield Road, Cambridge CB2 1 EWJohn C. Tebby. Department of Chemistry, North Staffordshire Polytechnic, College Road, Stoke-on-TrentST4 2DEEvidence that tertiary phosphine oxides and arenesulphonamides combine in a 1 : 1 molecular ratio to form stronglyhydrogen-bonded adducts, which do not dissociate in chloroform solution, is obtained from molecular weight,conductance, l H and 31P n.m.r., and i.r. spectral measurements. Tertiary phosphines and anhydrous Chloramine-Tgive phosphine imides, which in the presence of water are hydrolysed to give the corresponding phosphine oxidesand toluene-p-sulphonamide. Evidence is adduced supporting the six-membered, hydrogen-bonded, cyclicstructure (VIII) for these adducts.IN early investigations on the nature and polarity of theco-ordinate link, Mann 1 noted the difference in type ofproduct obtained when sodium N-chlorotoluene-9-sulphonamide (C hloramine-T) trih ydrat e reacted with(a) aliphatic sulphides, and (b) tertiary arsines (Scheme).(a) R2S + MeC,H,*SO,-NCINa I__t NaCl f R,S+N*SO,.C,H,Me(1)(11)(b) R3As + MeC,H,*SO,.NCINa + H,O +R,As(OH)-NH*SO,*C,H,MeSCHEMEReaction (a) proceeded rapidly and completely even whenthe liquid sulphide was shaken with a cold aqueous solu-tion of Chloramine-T.The product (I) was first termeda sulphilimine, and later a sulphinimine : it can be desig-nated as R,S=N-S0,*C6H,Me, one of the early examplesof a sulphurane.Reaction (b) also proceeded readilywith certain tertiary arsines, and the product (11) wasapparently similar in type to compounds such as (111),which are readily formed by the union of a tertiary arsineoxide and an acid such as nitric or picric acid; aliphatictertiary amine oxides readily give similar derivatives (IV) .R,N+(OH)X-(IV)R,P=N*SO,*C,H,Me R3P(OH).NH*S0,C,H,Me(V (VI)The reaction of tertiary phosphines in absolute ethanolwith anhydrous Chloramine-T was later studied by Mannand Chaplin.2 These phosphines (triphenylphosphineand various trialkylphosphines) usually gave phosphineimides (V); but the same reaction carried out in 98ethanol gave products which were named ' hydroxy-sulphonamides ' (VI), similar to the arsenic derivatives(11). The formation of these compounds was unexpected,for at that time the union of tertiary phosphine oxideswith acids to give stable products was rare, and unionwith so weak an acid as toluene-p-sulphonamide appearedimprobable. A detailed study was therefore made of theaction of Chloramine-T, in anhydrous conditions and inrectified spirit, on trisubstituted triphenylphosphines ;the o-, p-, and m- isomers of each phosphine were similarlyF.G. Mann, J. Chem. SOC., 1932, 958.F. G. Mann and E. J. Chaplin, J. Chem. Sac., 1937, 527.A. I?. Cameron, N. J. Hair, and D. G. Morris, Chem.SOC.Autumn Meeting, York, 1971; Chem. Comnt., 1971, 918.treated for comparison. The results are summarised inthe Table,2 and show that the position, rather than theInteraction of trisubstituted triphenylphosphines,P(C,H,X),, with Chloramine-T(a) AnhydrousChloramine-T in (b) Chloramine-T trihydrateX absolute ethanol in rectified spiritortho- Me Phosphine imide Phosphine imideMe0 Phosphine imide Phosphine imide + hydroxy-sulphonamideCl Phosphine imide Phosphine imidesulphonamidepara- Me Phosphine imide Phosphine imide + hydroxy-Me0 Phosphine imide Hydroxy-sulphonamideC1 Phosphine imide Phosphine oxide + toluene-sulphonamidemeta- Me Syrup Hydroxy-sulphonamideMe0 Glass H ydroxy-sulphonamideC1 Amorphous solid Phosphine oxide + toluene-sulphonamidenature, of the substituent determines the type ofproduct.The phosphine imide formulation (V) of the productsobtained from the reactions in absolute ethanol hassubsequently proved to be correct and recently the X-raystructure of triphenylphosphine 9-tolylsulphonylimide(V; R = Ph) has been dete~mined.~ However, com-parable studies of the nature of the so-called hydroxy-sulphonamide (VI; R = Ph) do not appear to have beenmade.Formulation of these compounds as hydroxy-phosphoranes, involving a pentacovalent phosphorusatom, appears improbable, especially in view of the factthat they can also be made by direct combination of atertiary arylphosphine oxide and toluene-p-sulphon-amide. Tertiary phosphine oxides are now known to belargely inert towards nucleophilic attack on phosphorus,except where the phosphorus atom is bound to stronglyelectron-withdrawing groups.4 Nucleophilic attack onphosphoryl phosphorus by toluene-9-sulphonamide toform, after subsequent protonation, a pentacovalenthydroxyphosphorane (VI) appears unlikely.Several of the ' hydroxy-sulphonamides ' prepared inthe original study have been re-examined. The proper-ties of the ' hydroxy-sulphonamide ' derived from tris-9-methoxyphenylphosphine and hydrated Chloramine-T inA.J. Kirby and S. G. Warren, ' The Organic Chemistry ofPhosphorus,' Elsevier, Amsterdam, 19672794 J.C.S. Perkin Iethanol are typical of the hydroxy-sulphonamides andwill now be discussed.Direct union of equimolar proportions of tris-fi-met hoxyphenylphosphine oxide and toluene-fi-sul-phonamide in toluene, gave an adduct identical with thatprepared via the phosphine and hydrated Chloramine-Tin ethanol. Molecular weight determinations showedthat the adduct was not dissociated to any significantextent in chloroform solution.31P N.m.r.studies of the adduct rule out a penta-covalent hydroxyphosphorane structure. The 31P spec-trum of the adduct in chloroform solution exhibited asignal at 6 -30 p.p.m. (relative to 85 H,PO,); thespectrum of the corresponding phosphine oxide exhibiteda signal at 8 -29.5 p.p.m., indicating that the shieldingof the phosphorus in the adduct is similar to that in thephosphine oxide, and different from the large positivechemical shifts generally observed for pentaco-ordinatephosphoranes.Alternative formulations for the adduct such as thehydroxyphosphonium salt (VII) , which could be con-sidered as being produced by dissociation of a pentaco-ordinate hydroxyphosphorane, were ruled out by theresults of conductance studies.A solution of the adduct(0.002~ in chloroform) had a very low conductivity com-pared with a similar solution of methyltriphenylphos-phonium iodide. In addition, the absence of the cationof (VII) was indicated when a deuteriochloroform solutionof t ris-$-met hox yphen ylphosphine oxide , when treatedwith sulphuric acid, failed to produce any shift in thelH n.m.r. signal due to the methoxy-groups.In view of the ease of formation of the adduct from thephosphine oxide and toluene-$-sulphonamide in toluenesolution, a hydrogen-bonded structure is most easily en-visaged. Recently, hydrogen-bonded adducts of tri-phenylphosphine oxide with N-methyltoluene-fi-sul-phonamide have been described: and similar hydrogen-bonded adducts of phosphine oxides with phenolsJ6 andalso with strong mineral acids,' have been reported.Thei.r. spectra of our adducts are in keeping with such ahydrogen-bonded structure ; for example, the spectrumof the adduct (VIII; Ar = fi-tolyl) shows vp=o 1165,whereas that of the corresponding phosphine oxide,(fi-tolyl),PO, shows vp=o 1190 cm-l. The N-H stretch-ing absorption in the free sulphonamide appears as adoublet at 3240 and 3330 cm-l, whereas in the foregoingadduct, it occurs as a broad band centred at 3260 cm-1.These findings support a N-H * 0-P hydrogen bond.The i.r.bands due to the sulphonyl group show marked- +5 V. A. Shokol, L. I. Maliakov. and G. J. Derkach, ZBur.6 M. Schindlbauer and H. Stenzenberger, Monatsh., 1968, 98,abshchei Khim., 1966, 86, 930 (Chem. Abs., 1966, 65, 12,229).2468.sharpening in the adducts. Together with the molecularweight measurements, this indicates that the adductsmay also contain a P - 0-S electrostatic interactionwhich would be present in an internally hydrogen-bonded structure such as (VIII). Similar interactionshave been observed in sulphonate phosphonium betaines?and in our adducts they would reinforce the hydrogen-bonding and explain the remarkable stability of theseadducts to dissociation.A hydrogen-bonded structureis also in keeping with the 1H and 3lP n.m.r. data on theadduct s.The cumulative physical evidence thus strongly indi-cates that these adducts have the six-membered hydro-gen-bonded ring system (VIII).+ - 4 -Me -+ Ar,P=N*SO*Me - Ar,PO+H,N*SO,The reaction of tertiary phosphines with Chloramine-Tis now interpreted in the following way (see Scheme) : inabsolute ethanol the weakly basic phosphine imide isobtained but in the presence of water this is rapidlyhydrolysed to the phosphine oxide and toluene-p-sulphonamide, which then unite to give the adduct (VIII).The results summarised in the Table show that thesusceptibility of the phosphine imide to hydrolysis is leastwhen ortko-substituents hinder the approach of water tothe P-N bond.On the other hand the stability of theadduct of the phosphine oxide and toluene-fi-sulphon-amide is least when the P-phenyl ring bears the electron-withdrawing chlorine atom. This latter observationsuggests that the chlorine atom increases the electron-deficiency of the phosphorus atom, which then demandsincreased donation of electrons from the oxygen atom,presumably mainly by fi,-d, bonding. This leads to aweaker hydrogen bond and possibly a weaker attractionbetween the phosphorus atom and sulphonate groups.For comparison with the foregoing phosphorus com-pounds, it may be noted that tris-(2-~hlorovinyl)arsinereacts with hydrated Chloramine-T to give an adduct oftype (11) ; triphenyl-, tri-o-tolyl-, and tri-p-tolyl-arsines react under strictly anhydrous conditions to givearsine imides, amp;As:N502*C,H,Me-P ; dimethylphenyl-arsine and methylphenethylphenylarsine react to givethe corresponding tertiary arsine oxides1D.Hadzi, J . Chem. SOC., 1962, 5128.8 M. A. Shaw, J. C. Tebby, R. S. Ward, and D. H. Williams,9 F. G. Mann and W. J. Pope, Traws. Chem. Soc., 1922, 121,J . Chem. SOC. ( C ) , 1968, 2795.17641972EXPERIMENTAL1H N.m.r. spectra were recorded a t 60 MHz on a Perkin-Elmer R 10 spectrometer with tetramethylsilane as internalstandard. 31P N.m.r. spectra were recorded at 24 MHz onthe same instrument, with 85 phosphoric acid as externalstandard. 1.r. spectra were recorded with a Perkin-Elmer350 spectrophotometer.Except where otherwise stated,the phosphine oxides and their adducts with toluene-p-sulphonamide were prepared as described by Mann andChaplin. Conductance measurements were carried out inchloroform solution, by use of a Lock conductance bridge.The Adduct (VIII ; Ar = p-MeOC,H,) .-Tris-9-methoxy-phenylphosphine oxide (0.368 g, 1 mmol) and toluene-p-sulphonamide (0.171 g, 1 mmol) were heated in toluene(10 ml). When cooled the solution deposited diamond-shaped crystals, m.p. 122-123', identical with the productisolated from the reaction of tris-p-methoxyphenylphos-phine and hydrated Chloramine-T in rectified spirit (lit.,2m.p. 121"), vmx, (mull) 3260br cm-l (NH), p-0 region com-plex, 7 (CDCI,) 2.1-3-25 (16H, m), 4.48 (2H, m), 6.22 (9H,s ) , 7.65 (3H, s), salP (CHCl,) -30 p.p.m.Found: C, 62.6;H, 5.6; N, 2.4 ; M (by ebulliometry in chloroform), 493.C,,H,,NO,PS requires C, 62.3; H, 5-6; N, 2.6; M , 5391.A 0.002M-solution of the adduct in chloroform had negligibleelectrical conductivity.Tris-p-methoxyphenylphosphine Oxide.-The oxide, m.p.142-143", had 6 31P (CHC1,) -29.5 p.p.m., T (CDC1,) 2.2-3.2 (12H, m) and 6.22 (9H, s) (the spectrum was unaffectedby the dropwise addition of sulphuric acid).The Adduct (VIII; Ar = O-MeO*C,H,).-The adduct,2795derived from tris-o-methoxyphenylphosphine and hydratedChloramine-T, had m.p. 151-152' (lit.,2 149'), vmX. (KBr)2940, 3395 (NH), and 1168 cm-l ( P O ) , 6 31P (CHC1,) -27Tras-o-methoxyphenyl~hosphine 0xide.The adduct (VIII ;Ar = o-MeO*C,H,) was triturated with aqueous 2~-sodiumhydroxide, and the liberated phosphine oxide was collectedand washed with water ; to ensure completion of the reactionthe oxide was moistened with ethanol and the triturationrepeated. The white oxide, when dried in vucuo at 80', hadm.p. 217-218' (lit.,lo m.p. 215-217'), 6 31P (CHC1,) -26.5p.p.m., T (CDC1,) 2.25-2.70 (6H, m, ArH) 2.90-3.20 (6H,m, ArH) 6.48 (9H, s, MeO) .The Adduct (VIII; Ar = m-MeO*C,H,).-The adductderived from tris-m-methoxyphenylphosphine oxide hadm.p. 1 1 4 1 1 5 deg; (lit.,2 112'), vmX (KBr) 3020, 3160, and 3310(NH), and 1165 and 1190 cm-l ( P O , SO), 6 31P (CHC1,)-31 p.p.m.Tris-m-rnethoxyphenylphosfihke 0xide.The oxide, m.p.154-155' (lit.,2 151-152') had 6 31P (CHCl,) - 30-5 p.p.m.The Adduct (VIII ; Ar = p-MeC,H,) .-The adduct derivedfrom tri-p-tolylphosphine oxide had m.p. 108" (lit.,2 106'),vmax. (KBr, mull, or chloroform) 3260br (NH) and 1165 cm-1( P O ) , T (CDCl,) 2.2-2.95 (16H, m) and 7-64 (12H, s),6 31P (CHC1,) -30.5 p.p.m.Tri-p-toZylphosphine 0xide.The oxide had 6 31P (CHC1,)- 30 p.p.m. and vp=o 1190 cm-1.2/995 Received, 4th May, 19721lo G. Wittig, H. D. Weigmann, and M. Schlosser, Chem. Bev.,P*P.rfl.1961, 94, 676
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