Jain, N. C.

Mehrotra, R. C.

Rai, A. K.

English

NOPR

Indian Journal of ChemistryVol. 14A, April 1976, pp, 256-259Alkoxide Complexes of Some Tri- & Tetra-valent Metals: Part 1-Conductometric & Potentiometric Studies on Some AluminiumAlkoxide Complexes in Non-aqueous SolventsN. C. JAIN, A. K. RAI & R. C. MEHROTRA*Department of Chemistry, University of Rajasthan, JaipurReceived 29 May 1975; accepted 27 October 1975The conductometric and potentiom.etric titrations of aluminium chloride and alkoxides(methoxide, ethoxide and Isopropoxide) with alkali metal (lithium, sodium and potassium)alkoxldes have been carded out in solvents like methanol, ethanol and isopropanol. The forma-tion of a number of species like AIC12(OR), AICl(OR)2' (AIOR)3 and M[At(OR).J have beendetected and confirmed. The effect of change in concentration of the reacting species, alkalirnetal ions and alkoxide groups on the formation of these species has also been investigatedand discussed.THE chemistry of a number of alkoxides anddouble alkoxides has been recently reviewedby Mehrotra and coworkers-A, In view ofsome interesting features like covalent behaviourof some double alkoxy derivatives of strongly electro-positi ve alkali metals, attempts have also beenmade to establish the stoichiometry of some of thesederivatives by titrimetric techniques using chemicalindicators=" or by physicochemical methods.tJ?Preliminary synthetic efforts'! showed thatamongst simple expected products, M[AI(OPri)4J(where M=Li, Na or K), the potassium derivativeappears to have unexpectedly highest solubilityin organic solvents. In view of this, conductometricand potentiometric titration techniques have beenemployed to detect the formation and stoichiometryof complex species in the reactions of aluminiumchloride or alkoxides with alkali metal alkoxidesin non-aqueous solvents. The effect of varyingconcentration of the reactants, change of solventand the nature of the alkali metal on the nature ofthe species formed during the reaction, has also beeninvestigated.Materials and MethodsAll titrations were carried out in a dry box underabsolutely anhydrous condition.Anydrous AICl3 (BDH) was resublimed beforeuse. AI(OPriJa was distilled under reduced pressure.Lithium, sodium and potassium metals (BDH)were used after cleaning the surface. Methanol,ethanol, isopropanol, benzene and acetic acid (BDH/SM) were dried by standard methods and distilledbefore use. KAI(OPri)4 and AI(OMeJa were synthe-sized as described in Iiteraturet--P.The conductivity measurements were carried outusing a TESLA conductivity bridge having a speciallyfabricated conductivity cell of cell constant 0·218 crrr".*Preseilt address; University of Delhi, Delhi.256E.M.F. and pH measurements were carried outon a Radiometer pH meter having glass and calomelcontaining saturated KCI solution in methanol asindicator and reference electrodes respectively.Results and DiscussionConductometric titrations of AlCl3 with MOR,where M =Li, Na or K; R=Me, Et or Pri in non-aqueous solvents - Dissolution of a white precipitate,which appears on addition of KOMe to a solutionof AIC13 (5·57 X 10-2M) in methanol continues upto the addition of one mole of KOMe per mole ofAIC13 and the conductivity value shows a continuousincrease up to one mole of KOMe (Fig. 1, curve A).This may be due to the solubility of the productsIa (or Ib) (Eqs. 1 and 2) and limited amounts ofKCI in MeOH.Further addition of KOMe solution shows a de-crease in conductivity and the formation of a bulkyprecipitate up to ",2·8 moles of KaMe/mole ofAICI3• This decrease may be due to the formationof insoluble Al(OMe)a and KCI (Eq. 3). Beyondthis, the flocculent precipitate dissolved and therewas an increase in conductivity.The second inflexion corresponded to the additionof ,...,3·8 moles of KOMe. The soluble species wasfound to be KAI(OMe)4 (Eq. 4).White crystalline particles left at the bottom of theconductivity cell were found to be KCI on analysis.Further addition of KOMe only increases the con-ductivity of the solution linearly and does notindicate the formation of any other higher ionicor covalent species.MeOHAiCI3+K+OMe- ---->- Al(OMe)Clz+K++CI- •.. (1)IaAI(OMe)CI2+xl\1eOH --+ [AI(OMe).xMeOHJ2++2Cl- ... (2)IbAl(OMe)CI2+2KOMe --+ AI(OMe). .\.+2KCI ~ (3)AI(OMe)3+K+OMe- "" [KAI(OMe).J "" K++[AI(OMe)J- (4)JAIN et al.: ALKOXIDE COMPLEXES OF TRi- & TETRA-VAL TINT METALS90807-0IeoTe5If')Qx~:~'0=>'0CoUIU;;:'0.,Q..If)E•o18 r IIe j'o er oe T145 9 es:11'1 0Q v~ 0X >. - >.10 £ '2 1x 'E0 ~ 0~ :I: 's (!)u Q) n Q)=> > >.. => ..'0 => '0 ::JC U c u6 0 5u ... 0 ..0 u IfI u,I.!:! o.•. ~'u o2 '" 3 Q)~ Q..If) If)oI·O~_.....,.~_--:,,-:-_~,-:-_~~_-=,~_-::::--_-:,:::--_--'O0·0 1'0 2'0 3'0 4·0 5'0 6{) 7·0I . [MOR]Mo or ratio AiCI3Fig. 1 - Concluctometric titrations of AICI. with MOR (where M = Li, Na and K; R = Me, Et arid Pri) [Curve(A) KOMe M/l'08 VS 25 ml of AICI. M/17'94 in MeOR; (B) KOMe M/l'02 vs 25 ml of AICl3 M/19·16+0·8 rnl ofKOMe M/l'02 in MeOR; (C) KOMe M/l·53 vs 25 ml of AICI. M/39'90 in MeOH; (D) LiOMe M/O·86.vs 25 mlof AICI. M/25'08+0'8 ml of LiOMe M/O'86 in MeOR; (E) NaOMe M/l'l1 vs 25 ml of AICI. 1.1/19'32 III MeOH;(F) KOMe M/O'96 vs 35 ml of AlCI. MI27'73+0'8 ml of KOMe MIO·96 in McOH (25 ml)+benzene (10 ml);(G) KOEt Mll·00 vs 25 ml of AICI. MI17'55+0'8 ml of KOEt M/l'OO in EtOR; (R) KOPri M11·17 vs 25 ml ofAlCI. MI22'00+ 1·0 ml of KOPri 1.111'17 in PriOR]Even on repeating the above titrations undervery carefully controlled conditions, the inflexionsat ",2·8 and ,....,3·8moles of KOMe per mole of AICl3remained unaltered. It was therefore, conjecturedthat this might be due to initial reaction of AIClawith solvent methanol to form a product of the typeAIC12'7·(OR)o·3.xROH similar to reactions of anhy-drous AfCl, with alcohols (MeOH, EtOH andPriOH)l3. In order to check this assumption, 0·5mole of KOMe was first added to AICla before dis-solving it into methanol. It was assumed that KOMewould have converted the AICla into AICb5 (OMe)o·5.Titration of this species with KOMe gave a titrationcurve (Fig. 1, curve B) almost similar to curve A exceptthat inflexion were seen at 3·0 and 4·0 moles of KOMeinstead of at 2·8 and 3·8 moles of KOMe in curve A.When a more dilute solution of AICla (2·51 X 10-2M) was titrated, the conductivity continuouslyincreased and only one inflexion point on the addi-tion of ,....,4·0moles of KOMe was observed (Fig. 1,curve C). The continuous increase in conductivitymay be due to KCl formed remaining soluble, asits concentration does not appear to increasethroughout the titration beyond its solubility limit.Therefore, the first and second inflexions obtainedin earlier cases could not be detected. Howeverthe precipitation and dissolution follows a patternsimilar to that observed with concentrated solutions.Titration of AICla solution with LiOMe (Fig. 1,curve D) shows only two inflexions instead of three(Fig. 1, curve A). The disappearance of the, ~~stinflexion point may be due to much higher solubilityof LiCl in MeOH . The two inflexions correspondto the reactions (5) and (6) respectively.. .The titration with N aOMe showed an mcrease mconductivity and only one inflexion at ,....,2·0 molesof NaOMe (Fig. 1, curve E) corresponding to theformation of AI(OMe)2Cl.In the titration of AICla with KOEt in ethanoli.csolution, the conductivity decreased up to the a~dl-tion of ,....,2·0 moles (Fig 1, curve G), then remamedconstant up to the addition of 3·0 moles of KOEtsolution and thereafter, started rising linearly. Theprobable reactions may be represented by Eqs. (7)and (8).The lower degrees of association of AlCI(OEt)2and AI(OEth in ethanol compared to those of AICl-(OMeh and Al(OMeh in methanol may be r~spon-sible for this behaviour, as no flocculent preCIpItatewas observed during the course of titration. TheAICI.+3LiOMe ~ Al(OMcls+3LiCl (5)AI (OMeJa + LiOMe ~ [LiAl(OMe).] ~ Li++[AI(OMe).r (6)AICl.+2KOEt -+ AlCl(OEt12+2KCI ~ (7)AICI(OEt12+KOEt-+ AI(OEtls+KCI ~ (8)257INDIAN j. CHEM., VOt. 14A, APRIL 191606754 ECJ7Es:50 0vQ)(;>.46 .~;CJ~Co42 c.:!100-'u(IIQ.38 enMolar-ratio [ArCI3]MORL-__~ -L -L ~ ~ ~ ~34o O·t 0'2 0·3 0-4 0'5 0'6(}6Fig. 2 - Potentiometric and conductometric titrations of 25 ml of MOR with AICI, in ROH (where M = Li, Na and K;R = Me rvnd Et) [Potentiometric titrations : Curve (A) AICI, M19'04 vs KOMe M/12·51 in MeOH; (B) AICI, M19'79 vsKOMe M/ll'62 in MeOH; (C) AICl, MIS·51 vs NaOMe M/I0'16 in MeOH; (D) AICI. M/11'S5 vs LiOMe MIS'3S in MeOH;(E) AICI,M/16'93 vs KOEt M/ll'06 in EtOH. Conductometric titrations : (F) AICI,M17'13 VS KOMe M/ll'54 in MeOH]much lower solubility of KCI in ethanol (0·7 g/litre)compared to that in methanol (3·4 g/litre) wouldalso lead to the observed differences in the titrationcurves.The titration of AICla with KOPri in isopropanolfollows a pattern (Fig I, curve H) similar to thatobserved with KOEt.The titration of AICla solution in a mixture ofmethanol (10 ml) and benzene (15 ml) media withKaMe follows a different pattern (Fig. I, curve F)and formation of only one species, AI(OMeJa couldbe detected. This difference can be understoodin view of the lower solubility of KCI in methanol-benzene mixture compared to that in methanolalone.Reverse conductometric titration oj KOMe withAleta in anhydrous methanol - As expected, twoinflexions corresponding to the molar ratios of 0·25:1·00 and 0·33: 1·00 (AICla: KaMe) were observed.When AICla was added to KaMe in methanol (Fig.4, curve F), the precipitation starts after the firstinflexion point and is complete near the secondinflexion point. The probable reactions may berepresented by Eqs. (9) and (10).Conductometric titration oj 1:4 mixture oj Al(OMelaand KOMe with acetic acid and hydrogen chloridein methanol- In order to confirm the above conclu-sions, the back titration of KAI(OMe)4 in the4K+(OMet+AICI. -+ [KAI(OMe).J+3KCI3[KAI(OMe)~]+AICI3-+ 4AI(OMe), t +3KCI... (9)... (10)258presence of excess (3 moles) of KaMe was carriedout with acetic acid and hydrogen chloride inmethanol.In the titration with acetic acid the conductivitydecreased up to the addition of 3 moles of the acid,indicating the neutralization of 3 moles of KaMetaken in excess (Eqs. 11 and 12).The conductivity decreased further on the addi-tion of acetic acid and a white precipitate correspond-ing to the stoichiometry of AI(OMe)a, seperated outafter the addition of 4 moles of acetic acid (Eq. 13).The conductivity increased up to the additionof 6 moles of acetic acid and thereafter becameconstant.The titration when repeated with methanolichydrogen chloride solution (Fig. 2, curve B) showeda continuous decrease in conductivity and the firstinflexion corresponding to the neutralization of addedKaMe (4 moles) was observed. The second inflexionobtained on further addition of HCI solution may bedue to the formation of AICI2(OMe) species. Theprobable reactions may be as shown in Eqs. (14-16)MeOHAI(OMe)3+4KOMe~KAI(OMe)&+3KOMe ... (11)MeOH3KOMe+ 3CH3COOH---+3CH,COOK + 3MeOH ... (12)MeOHKAI(OMe).+CH,COOH~H3COOK+ Al(OMe)3.j.+MeOH ... (13)flexions in concentrated as well as in dilute solutions(Fig. 2, curve B).Unlike conductometric titration curves changeof alkali metal from Li to Na or K in MOMe hadno affect on the nature of titration curve (Fig. 2,curves C and D).The different alkali methoxides show the formationof two different species at all concentrations, whereasthe formation of only AI(OEt)a could be detected inthe titration of KOEt with AICla in ethanol (Fig. 2,curve E). The titration of KOPri with AICl3 inisopropanol could not be accomplished due to poorsolubility of AICl3 in isopropanol.Titrations of AICl3 with KOMe in methanol orKOEt in ethanol show the formation of only onespecies, i.e. AI(ORhAcknowledgementThanks are due to CSIR, New Delhi for the awardof a junior research fellowship to one of them (N.C.]')JAIN et al.: ALKOXIDE COMPLEXES OF TRl- & TETRA-VALENT METALSA!(OMe)s+4KOMe ...•.KAl(OMe).+3KOMe ... (14)KAl(OMe).+3KOMe+4HCl->-Al(OMe)3 t +4MeOH+4KCI... (1 5)AI(OMe)s+2HCl->- AlCl.(OMe)+2lVIeOH ... (16)PriOHAl(OPri)3+KOPri "" KAl(OPri). ... (17)The difference in behaviour is due to the strongacidic character of HCI in comparison to aceticacid.The formation of AICI2(OMe) species was furthercon~rmed in a dir~ct titration of AI(OMe)3 suspend-ed m methanol with HCI solution.Conductometric titrations between aluminium alko-xides and potassium alkoxides - No inflexion was?bserved in the titration of AI(OMels with KOMein methanol. However, when KOPri was addedto AI(OPri)3 solution in isopropanol, an inflexionat 1: 1 molar ratio, indicating the possibility of aweak complex (Eq. 17), was obtained.No definite inflexion was however obtained inthe reverse titration. 'Potentiometric titrations of MOR with AlCI inROH where M =Li, Na or K; R=Me or Et _3Theuse 0.£ glass electrodes in non-aqueous solvents hasbeen mtroduced s~ccessfully by different workers14,15.In the present mvestigations, the electrochemicalcell of the type (A) was set up for the measurementof pH and e.m.f. of solution mixtures.Hg I Hg2C13+ KCl II KCl I' Solution I Glasssatd (H20) satd (lVIeOH) I studied electrode(AlTwo sharp inflexions (Fig. 2, curve A) wereobtained on titrating KOMe with AICI3• Theexact positions of inflexions were calculated by plot-ting a graph between I1Ejl1V (or 112Ejl1V2) versusvolume of AICl3 solution added. The inflexionpoints corresponded to the addition of 0·25 and 0·33mole of AICl3 per mole of KOMe solution, confirm-ing the formation of KAI(OMe)4 and Al(OMe)3 species.It may be pointed out that contrary to theobservations in conductometric titrations, poten-tiometric titration technique showed similar in-References1. KAPOOR, P. N. & lVIEHROTRA,R. C., Coord. Chem. Rev.,14 (1974), 1.2. lVIEHROTRA,R. C. & lVIEHROTRA,A., Lnorg ; chim, ActaRev., 5 (1971), 127.3. lVIEERWEIN,H. & BERSIN, T., Liebig's Ann., 476 (1929),113.4. JONES, R. G., BINDSCHADLER,E., BLUME, D., lVIARTIN,G. A., THIRTLE, j. R. & GILMAN, H., J. Am. chem,Soc., 78 (1956), 6027.5. BARTLEY, W. G. & WARDLAW,W., J. chem. Soc., (1958),422.6. CARTER, D. G., Titanium alhoxides, Ph.D. thesis, Univer-sity of London, London, 1959.7. GUT, R., Helv. chim. Acta, 47 (1964), 2262.8. LUDMAN,C. J. & WADDINGTON,T. C., J. chem, Soc. (A),(1966), 1816.9. lVIEHROTRA,R. C. & AGARWAL,M. M., J. chem. Soc. (A),(1967), 1026.10. BIANCO, P., HALADJIAN, J., PILARD, R. & Asso, L.,J. electroanal, Chem., 49 (1974), 273.11. AGARWAL, M. M., Double alhox ides of some tri- andtetravalent metals, Ph. D. thesis, University of Raja-sthan, Jaipur, 1968.12. MEHROTRA, R. C., J. Indian chem, Soc., 31 (1954), 85.13. FUNK, H., SCHORMULLER, J. & HENSINGER, w., Z.anorg, allg. Chem., 205 (1932), 361.14. STOCK, J. T. & PURDY, W. C., Chem. Rev., 57 (1957),1159.15. TOREN, E. C., (Jr.), Analyt. cu-«, 40 (1968), 402.259

Alkoxide Complexes of Some Tri- & Tetra-valent Metals: Part I- Conductometric & Potentiometric Studies on Some Aluminium Alkoxide Complexes in Non-aqueous Solvents

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Alkoxide Complexes of Some Tri- & Tetra-valent Metals: Part I- Conductometric & Potentiometric Studies on Some Aluminium Alkoxide Complexes in Non-aqueous Solvents

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