Hydrogen Bonding Interaction between 1-Propanol and Acrylic Esters in Non-polar Solvents: An FTIR Study

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1 RESEARCH ARTICLE K. Dhrmlingm, K. Rmchndrn nd P. Sivgurunthn, 75 S. Afr. J. Chem., 26, 59, 75 81, Hydrogen Bonding Interction between 1-Propnol nd Acrylic Esters in Non-polr Solvents: An FTIR Study Kurunthu Dhrmlingm, Krishnmurthy Rmchndrn nd Periysmy Sivgurunthn* Deprtment of Physics, Annmli University, Annmli Ngr, Tmilndu-682, Indi. Received 22 August 25; revised 1 June 26; ccepted 19 June 26. ABSTRACT The ssocition between 1-propnol nd crylic esters (methyl methcrylte, ethyl methcrylte nd butyl methcrylte) in non-polr solvents, viz. n-heptne,, nd benzene hs been investigted by mens of FTIR spectroscopy. The formtion constnts of the 1:1 complexes hve been clculted using Nsh s method. The vlues of the formtion constnt nd the Gibbs energy vry with ester chin length, which suggests tht the strengths of the intermoleculr OH O=C bonds re dependent on the lkyl group of the crylic ester nd the results show tht the proton ccepting bility of crylic esters is in the order methyl methcrylte < ethyl methcrylte < butyl methcrylte. The results lso show significnt dependence of the ssocition constnt upon the solvent used. The solvent effect on the hydrogen bond equilibri is discussed in terms of specific interctions between the solute nd the solvent. KEYWORDS FTIR spectroscopy, crylic esters, hydrogen bonding, solvent effects. 1. Introduction Acrylic esters re industrilly importnt chemicls nd precursors in the synthesis of polymers. 1 Alcohols ply n importnt role in mny chemicl rections due to their bility to undergo self-ssocition with mnifold internl structures. Experimentl investigtion of the spectroscopic properties of orgnic compounds is of gret vlue in understnding the nture of complex formtion between the molecules. Solvent effects ply n importnt role in orgnic rectivity phenomen, such s chemicl equilibri, the rtes of chemicl rections, polymeriztion, nd so on. Recently solvent effects on the infrred spectr of binry systems of MMA with orgnic solvents to investigte solute solvent interctions were extensively reported by Zheng et l. 2 nd Liu et l. 3 Recently our reserch group hs investigted the complex formtion of crylic esters with proton donors (lcohols) in non-polr solvents using FTIR spectroscopic 4 11 nd dielectric 12 methods. The complex formtion hs been interpreted in terms of formtion constnts. Thus, the study nd knowledge of the spectroscopic properties of binry nd ternry mixtures of crylic esters with polr ssociting liquids (lcohols) in nonpolr solvents is expected to provide useful nd vitl process prmeters for the efficient design of trnsesterifiction processes of industril interest. Keeping both the industril nd scientific interests in mind, n ttempt hs been mde in the present work to study the hydrogen bonding between the hydroxyl group of 1-propnol nd the crbonyl groups of crylic esters in non-polr solvents nd to elucidte the effect of the medium, nd prticulrly the role of specific solute solvent interctions on the stbility of 1:1 complexes, s well s on the hydrogen bond formtion between the hydroxyl group of 1-propnol nd the crbonyl groups of crylic esters using FTIR spectroscopy. 2. Experimentl A Nicolet Avtr 36 FTIR spectrometer with resolution of * To whom correspondence should be ddressed. E-mil: sivtmil21@yhoo.com c. 1cm 1 ws used. Spectr were recorded t room temperture (25 C) in the region of 4 to 4 cm 1 nd NCl cell of pth length.1 mm ws used. The spectrometer possesses utolign energy optimiztion nd dynmiclly ligned interferometer. It is fitted with KBr bem splitter, DTGS detector nd n Everlgo mid-ir source. A bseline correction ws mde for the spectr recorded. The pek intensities (bsorbnces) were clculted by the formul Absorbnce = log 1(I /I), where (I /I) is the rtio of the intensity of the incident light to the trnsmitted light. Methyl methcrylte (MMA), ethyl methcrylte (EMA) nd butyl methcrylte (BMA) with purity >99% were purchsed from Aldrich nd were used without further purifiction. AR grde n-heptne,, benzene nd 1-propnol were purified by stndrd methods. 13,14 3. Results nd Discussion The observed spectroscopic dt of 1-propnol in non-polr solvents (n-heptne, nd benzene) re provided in Tble 1. 1-Propnol in non-polr solvents exhibits two hydroxyl bnds in the region of cm 1 ; shrp pek bove 36 cm 1 is scribed to the OH stretching vibrtions of the free OH bond of lcohol molecules nd the second bnd ner 335 cm 1 is due to polymeric (hydrogen bonded) bsorption. 15 The position of the monomeric OH bsorption bnd nd the wvenumber difference between the monomeric OH (ν f ) nd the bonded OH (ν b ) bnds (i.e. ν = ν f ν b ) re observed in the solvent order Tble 1 Spectroscopic dt of 1-propnol in non-polr solvents. Solvent ν f /cm 1 ν b /cm 1 ν /cm 1 n-heptne benzene

2 RESEARCH ARTICLE K. Dhrmlingm, K. Rmchndrn nd P. Sivgurunthn, 76 S. Afr. J. Chem., 26, 59, 75 81, n-heptne > crbon tetrchloride > benzene. An immedite observtion is tht the wvenumber of the free OH bnd decreses with the polrizbility of the solvent, indicting tht intermoleculr interction between 1-propnol nd solvent molecules increses with increse of the polrizbility of the solvent. This demonstrtes tht the wvenumber of the free OH bnd is very sensitive to the solvent environment. A hydrogen bonded OH bsorption bnd round 3354 cm 1 is observed for the 1-propnol with n-heptne nd 1-propnol with crbon tetrchloride systems. In the cse of the 1-propnol with benzene system n bsorption bnd is observed t 3447 cm 1. 11,16 Benzene produces lower free OH stretching wvenumbers thn the other solvents due no doubt to the tendency for ssocition with the π electrons of the romtic ring. It is generlly found tht the positions, intensities nd shpes of bsorption bnds re influenced by solvents of different polrity. As the polrity of the solvent increses the OH stretching wvenumber decreses; this is due to stronger polriztion of the OH bond, which leds to decrese of the OH bond stretching force constnt. It is pprent tht the solvent environment hs strong determining effect on the wvenumber of the donor OH group, similr effect hving been observed by Bellmy et l. 17,18 These results fully confirm tht the solvent shifts of OH stretching vibrtions re primrily due to locl ssocition effects with solvent molecules. The bove observtion suggests tht solute solvent interction exists for the 1-propnol + benzene nd 1-propnol + crbon tetrchloride systems, i.e. n interction between the π-electrons in the benzene ring with H δ+ in 1-propnol nd with Cl δ in crbon tetrchloride with H δ+ in 1-propnol. No such interction is possible in the 1-propnol + n-heptne system. 19 The infrred dt of methyl methcrylte (MMA), ethyl methcrylte (EMA) nd butyl methcrylte (BMA) in non-polr solvents re given in Tble 2. The position of the crbonyl bsorption bnd of crylic esters in non-polr solvents is observed in the ester order methyl methcrylte > ethyl methcrylte > butyl methcrylte nd in the solvent order n-heptne > > benzene. 2 The higher wvenumber vlues of crylic esters + n-heptne thn crylic esters + crbon tetrchloride nd crylic esters + benzene indicte the bsence of specific solute solvent interctions. This observtion suggests tht specific interctions occur between the π* orbitls in crylic esters nd the lone pir electrons of Cl, or between the lone pir electrons of the >C=O group in esters nd the empty d-orbitls in the chlorine toms of crbon tetrchloride, or the lone pir of electrons in the crbonyl oxygen tom of crylic esters nd the π* orbitls of benzene. Similr results re reported by Oswl et l. 21 For ternry mixtures, the proton cceptor (crylic ester) concentrtion ws fixed t.5 mol dm 3 nd the proton donor (lcohol) concentrtion vried from.5 to.15 mol dm 3 in steps Tble 2 Spectroscopic dt of crylic esters in non-polr solvents. Acrylic ester Solvent ν c=o /cm 1 MMA n-heptne benzene 1724 EMA n-heptne benzene 1717 BMA n-heptne benzene 1716 Figure 1 Absorbnce versus concentrtion for methyl methcrylte with 1-propnol. Figure 2 Absorbnce versus concentrtion for ethyl methcrylte with 1-propnol. Figure 3 Absorbnce versus concentrtion for butyl methcrylte with 1-propnol. of.2 mol dm 3. The OH bnd intensity nd hlf-bnd width increse with incresing lcohol concentrtion but the reverse trend is observed for the crbonyl bsorption bnd (Tbles 3 11 nd Figs 1 3). This observtion indictes tht there is 1:1 complex formtion between the hydroxyl nd crbonyl groups, i.e. (OH O=C). 4 12,22 Utilizing Nsh s 23 method, the formtion constnts K ssocited with the hydrogen bonding process were determined. In this method t low concentrtion of lcohol the influence of the higher order complexes on the bsorption spectrum of the bse is neglected. The concentrtions of the proton donor [A], proton cceptor [B] nd complexed species [AB] involved in the interction re ssumed to obey Beer s lw t given chrcteristic wvenumber of the 1:1 complex. The totl bsorbnce of B per unit pth length is given by A= ε b [B] + ε b [AB] (1) where ε b nd ε b re the molr bsorptivities of the monomer species B nd the complexed species AB respectively. In the bsence of complexing gent, A, the totl bsorbnce per unit pth length is given by = ε b [B ] (2) where [B ] is the initil concentrtion of B. Dividing Eq. (1) by Eq. (2) [ B] [ AB] εb = + (3) [ B ] B ε b

3 RESEARCH ARTICLE K. Dhrmlingm, K. Rmchndrn nd P. Sivgurunthn, 77 S. Afr. J. Chem., 26, 59, 75 81, Tble 3 Absorbnce vlues of OH nd C=O bsorptions of 1-propnol nd methyl methcrylte in n-heptne for different concentrtions of /mol dm 3 OH bnd of 1-propnol C=O bnd of MMA in the OH bnd of 1-propnol in the C=O bnd of MMA in the in the bsence of MMA bsence of 1-propnol presence of MMA presence of 1-propnol Tble 4 Absorbnce vlues of OH nd C=O bsorptions of 1-propnol with methyl methcrylte in for different concentrtions of 1-propnol nd in the bsence nd presence of 1-propnol. /mol dm 3 OH bnd of 1-propnol C=O bnd of MMA in the OH bnd of 1-propnol in the C=O bnd of MMA in the in the bsence of MMA bsence of 1-propnol presence of MMA presence of 1-propnol Tble 5 Absorbnce vlues of OH nd C=O bsorptions of 1-propnol with methyl methcrylte in benzene for different concentrtions of /mol dm 3 OH bnd of 1-propnol C=O bnd of MMA in the OH bnd of 1-propnol in the C=O bnd of MMA in the in the bsence of MMA bsence of 1-propnol presence of MMA presence of 1-propnol The formtion constnt K my be defined s AB K = [ ] (4) [ A][ B] Combining Eqns. (3) nd (4) α [ B] ε b = α KA [ ] [ B ] ε b Introducing the conservtion of species B [B ]= [B] + [AB] (6) Invoking Eq. (4), [ B] = ( KA [ ]) [ B ] 1 When Eq. (7) is substituted into Eq. (5) εb KA [ ] α εb = α KA [ ] Tking (5) (7) (8) = z (9) K ε b = α (1) εb nd [ A] = 1 y Eq. (8) becomes α y z = (11) K y zk α y = (12) 1 z Expressing x = 1 1 z

4 RESEARCH ARTICLE K. Dhrmlingm, K. Rmchndrn nd P. Sivgurunthn, 78 S. Afr. J. Chem., 26, 59, 75 81, Tble 6 Absorbnce vlues of OH nd C=O bsorptions of 1-propnol with ethyl methcrylte in n-heptne for different concentrtions of /mol dm 3 OH bnd of 1-propnol C=O bnd of EMA in the OH bnd of 1-propnol in the C=O bnd of EMA in the in the bsence of EMA bsence of 1-propnol presence of EMA presence of 1-propnol Tble 7 Absorbnce vlues of OH nd C=O bsorptions of 1-propnol with ethyl methcrylte in for different concentrtions of 1-propnol nd in the bsence nd presence of 1-propnol. /mol dm 3 OH bnd of 1-propnol C=O bnd of EMA in the OH bnd of 1-propnol in the C=O bnd of EMA in the in the bsence of EMA bsence of 1-propnol presence of EMA presence of 1-propnol Tble 8 Absorbnce vlues of OH nd C=O bsorptions of 1-propnol with ethyl methcrylte in benzene for different concentrtions of 1-propnol nd in the bsence nd presence of 1-propnol. /mol dm 3 OH bnd of 1-propnol C=O bnd of EMA in the OH bnd of 1-propnol C=O bnd of EMA in the in the bsence of EMA bsence of 1-propnol in the presence of EMA presence of 1-propnol x = 1 since z = where nd re the bsorbnces of the crbonyl bnd of the crylic ester in the presence nd bsence of lcohol respectively. Eq. (12) my be rewritten in the form of liner eqution s y = x(k α) K (13) The physicl significnce of Eq. (13) is tht when the reciprocl of the donor concentrtion is plotted ginst the reciprocl of one minus the bsorbnce rtio the ppernce of stright line indictes 1:1 complex formtion, nd the intercept of the plot gives the negtive vlue of the formtion constnt. The grphs re shown in Figs 4 6. The Gibbs energies, G, of the systems were clculted using the following reltion 24 G = RT ln K (14) where R, T nd K represent the universl gs constnt, the bsolute temperture nd the formtion constnt of the hydrogen bonded complex, respectively. The formtion constnts nd the Gibbs energy vlues for ll the systems studied re provided in Tble 12. It is evident from Tble 12 tht the strength of the intermoleculr hydrogen bond formed between C=O group nd n OH group, i.e. OH O=C, is dependent on the bsicity of the C=O group. In this study the bsicity of the C=O group increses in the order methyl < ethyl < butyl methcrylte. This is becuse the negtive inductive effect of the lkyl groups increses in the order methyl to butyl, nd the electron contribution of the butyl group to the C=O group is significntly greter thn tht of the methyl group. Therefore, one would expect tht the strongest intermoleculr hydrogen bonds would be formed between the C=O group of butyl methcrylte nd the OH group of propyl lcohol nd the wekest between the C=O group of methyl methcrylte nd the OH group of propyl lcohol. 21 It hs been found tht two opposing effects, nmely specific

5 RESEARCH ARTICLE K. Dhrmlingm, K. Rmchndrn nd P. Sivgurunthn, 79 S. Afr. J. Chem., 26, 59, 75 81, Tble 9 Absorbnce vlues of OH nd C=O bsorptions of 1-propnol with butyl methcrylte in n-heptne for different concentrtions of /mol dm 3 OH bnd of 1-propnol C=O bnd of BMA in the OH bnd of 1-propnol in the C=O bnd of BMA in the in the bsence of BMA bsence of 1-propnol presence of BMA presence of 1-propnol Tble 1 Absorbnce vlues of OH nd C=O bsorptions of 1-propnol with butyl methcrylte in for different concentrtions of 1-propnol nd in the bsence nd presence of 1-propnol. /mol dm 3 OH bnd of 1-propnol C=O bnd of BMA in the OH bnd of 1-propnol in the C=O bnd of BMA in the in the bsence of BMA bsence of 1-propnol presence of BMA presence of 1-propnol Tble 11 Absorbnce vlues of OH nd C=O bsorptions of 1-propnol with butyl methcrylte in benzene for different concentrtions of /mol dm 3 OH bnd of 1-propnol C=O bnd of BMA in the OH bnd of 1-propnol in the C=O bnd of BMA in the in the bsence of BMA bsence of 1-propnol presence of BMA presence of 1-propnol interctions between the ester nd the OH group of the lcohol, nd non-specific dispersion interctions, i.e. breking of intermoleculr hydrogen bonds in the lcohol re possibly opertive in these mixtures. It is evident from Tble 12 tht the formtion constnts nd Gibbs energies for hydrogen bond formtion of crylic esters with 1-propnol in non-polr solvents re quite high for benzene. Next in order comes, while for n-heptne the equilibrium constnt nd Gibbs energy vlues re lowest. It my therefore be suggested tht the lowering of the formtion constnt in the bove order is due to the locl solvent interctions with 1-propnol in the order benzene > > n-heptne. The higher vlues of K in benzene solutions suggest tht, besides structure disruptions, wek but specific interctions of the OH π type occur between the hydroxyl group of 1-propnol nd the π electrons of the romtic ring, which is in greement Tble 12 Formtion constnts, K, nd Gibbs energies, G, for crylic esters with 1-propnol in non-polr solvents. Proton K /dm 3 mol 1 - G /kj mol 1 cceptor n-heptne Benzene n-heptne Benzene MMA EMA BMA

6 RESEARCH ARTICLE K. Dhrmlingm, K. Rmchndrn nd P. Sivgurunthn, 8 S. Afr. J. Chem., 26, 59, 75 81, Figure 4 Formtion constnts of 1:1 complexes of methyl methcrylte with 1-propnol in () n-heptne, (b) nd (c) benzene determined by Nsh s method t 298 K. Figure 5 Formtion constnts of 1:1 complexes of ethyl methcrylte with 1-propnol in () n-heptne, (b) nd (c) benzene determined by Nsh s method t 298 K. with the observtion of low OH stretching wvenumbers with specific interction with the solvent molecules present. The opposite effect is shown by n-heptne. This molecule would tend to solvte the ssocited complex due to its lrge size compred with tht of benzene nd would tend to oppose the formtion of the ssocited groups with the cceptors, giving rise to the low formtion constnts observed. Intermedite between these two groups re ssocition in the so-clled inert solvent,, which llows solvent ssocition by interction with specific groups of the solvent molecules, such s the CCl bonds. This observtion is in close greement with tht of Sivgurunthn et l. 11 for the 1-butnol ethyl methcrylte system in different solvents. 4. Conclusions The formtion constnts nd Gibbs energies of 1-propnol with crylic esters (methyl methcrylte, ethyl methcrylte nd butyl methcrylte) in non-polr solvents (n-heptne, nd benzene) were determined. From this study, it my be concluded tht the strength of the intermoleculr OH O=C bond formed between 1-propnol nd the crylic esters is dependent on the lkyl chin length of the crylic esters nd prllels the bsicity of the crylic esters, nd the hydrogen bonding between lcohols nd crylic esters in solution is complicted, depending not only on the cidity nd bsicity of the intercting components, but lso on the solvent properties. References 1 N. Hdjichrisridi nd N.L.J. Fetters, Mcromolecules, 1984, 17, J.P. Zheng, Q. Liu, H. Zhng nd D.J. Fng. Spectrochim. Act A, 24, 6, Q. Liu, J. Zheng nd D.J. Fng, Spectrosc. Lett., 24, 37, Figure 6 Formtion constnts of 1:1 complexes of butyl methcrylte with 1-propnol in () n-heptne, (b) nd (c) benzene determined by Nsh s method t 298 K.

7 RESEARCH ARTICLE K. Dhrmlingm, K. Rmchndrn nd P. Sivgurunthn, 81 S. Afr. J. Chem., 26, 59, 75 81, 4 P. Sivgurunthn, K. Dhrmlingm nd K. Rmchndrn, Z. Phys. Chem., 25, 219, P. Sivgurunthn, K. Dhrmlingm nd K. Rmchndrn, Spectrochim. Act A, 26, 64, P. Sivgurunthn, K. Dhrmlingm nd K. Rmchndrn, Indin J. Pure Appl. Phys., 25, 43, K. Dhrmlingm, K. Rmchndrn, P. Sivgurunthn nd G.M. Klmse, Min Group Chemistry, 25, 4, K. Dhrmlingm nd K. Rmchndrn, Phys. Chem. Liq., 26, 44, P. Sivgurunthn, K. Dhrmlingm nd K. Rmchndrn, Indin J. Phys., 25, 79, K. Dhrmlingm, K. Rmchndrn nd P. Sivgurunthn, Spectrochim. Act A, in press. 11 P. Sivgurunthn, K. Dhrmlingm nd K. Rmchndrn, Z. Phys. Chem., 25, 219, P. Sivgurunthn, K. Dhrmlingm, K. Rmchndrn nd G.M. Klmse, Min Group Chemistry, 25, 4, A. Weissberger, Techniques of Orgnic Chemistry, Wiley Interscience, New York, NY, USA, 197, pp J.R. Riddick nd W.B. Bunger, Orgnic Solvents, Wiley Interscience, New York, NY, USA, 197, pp J.L. Kirsch nd D.R. Coffin, J. Phys. Chem., 1976, 8, D.A. Ibbitson nd L.F. Moore, J. Chem. Soc. B, 1967, L.J. Bellmy, C.P. Conduit, R.J. Pce nd R.L.Willims, Trns. Frdy Soc., 1959, 55, L.J. Bellmy, H.E. Hllm nd R.L. Willims, Trns. Frdy Soc., 1958, 54, K. Grbdu nd B.B. Swin, Indin J. Pure Appl. Phys., 1993, 31, R.A. Nyquist, S. Fiedler nd R. Streck, Vib. Spectrosc., 1994, 6, S.L. Oswl, B.M. Ptel, A.M. Ptel nd N.Y. Ghel, Fluid Phse Equilib., 23, 26, H.F. Smith nd A.S. Rosenberg, J. Chem. Soc., 1963, C.P. Nsh, J. Phys. Chem., 196, 64, S.N. Vinogrdov nd R.H. Linnell, Hydrogen Bonding, Vn Nostrnd Reinhold Compny, New York, NY, USA, 1971, pp

Molecular interaction studies of acrylic esters with alcohols

Indian Journal of Pure & Applied Physics Vol. 43, December 2005, pp. 905-90 Molecular interaction studies of acrylic esters with alcohols P Sivagurunathan*, K Dharmalingam & K Ramachandran Department of