Studies in hydrogen-bond formation and adsorption of organic substances

Jain, S. K (1957) Studies in hydrogen-bond formation and adsorption of organic substances. PhD thesis, University of Glasgow.

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A study is presented of the forces involved in adsorption from solution with particular reference to hydrogen bonds and electrostatic attraction. In the first part, the refractive index method is used to detect intra- as well as inter-molecular complexes, particularly of hydrogen bond type, between simple organic compounds in aqueous and non-aqueous solution. The reality of the existence of such complexes is demonstrated by infrared spectrophotometry, molecular weight determinations, and by various comparisons of physical properties. The mechan-ism of adsorption of dyes by various fibres has been considered in the light of the results obtained. The following are some of the conclusions reached: (i) Water has a protective effect on certain groups, e.g., on the carbonyl group, on hydroxyl groups in some alcohols, etc. so that certain types of hydrogen bond do not form in aqueous solution. (ii) The hydroxyl group in alcohols is monofunctional and when present on vicinal carbon atoms forms weak five-membered chelate rings, e.g. in ethylene glycol or glycerol, (iii) The aldehyde group can act both as hydrogen-acceptor and hydrogen-donor. (iv) Carbohydrates normally exist in the ring form in aqueous solution and the hydroxy-groups are then protected by the solvent. The oppn-chain form reacts with pyridine or triethylamine. (v) In ethylene glycol, as a solvent, all the hydroxy-groups of the carbohydrates are reactive. (vi) The keto-group behaves bifunctionally as a hydrogen-acceptor though it is unreactive in water, ether or benzene. (vii) The reactivity of nitrogen-containing compounds suggests that the unsubstituted or N-monosubstituted amides exist in an enol-form in non-aqueous solution, but in aqueous solution the keto-form predominates. (viii) In sulphonated azo-compounds the azo-group is inactive towards alcoholic groups in aqueous solution. (ix) Esters, besides being hydrogen-acceptors, also act as hydrogen-donors, probably the hydrogen atom on the carbon being that involved in the complex formation. This is considered to show that adsorption by cellulose acetate and Terylene fibre may depend on this form of bonding. (x) The reactions of N-acetylglucosamine show that the adsorption on chitin is influenced by the hydrogen-bond formation. (xi) It has been concluded from the non-reactivity of the hydroxy-groups of carbohydrates in water that adsorption on cellulosic fibres from aqueous solution cannot be due to hydrogen-bonding. The refractive index method was also used to determine the importance of hydrogen-bonding by phenoxyacetic acids, in their activity as plant hormones. Unfortunately time did not permit this work to be completed. However, it was noticed that a hydrogen atom on the carbon atom adjacent to the carboxylic group is reactive and its absence in e.g. phenoxyisobutyric acid may be the cause of its inactivity as a growth-promoting agent. A study of the adsorptive properties of haematoxylin, a natural colouring matter has also been made. This dye is adsorbed by many different types of fibre. The apparent heats of adsorption and affinities for different fibres are reported. Adsorption on cellulose is probably due to van der Waal's attraction, while on wool, nylon, and cellulose acetate it is due to hydrogen bond formation. The adsorption of basic dyes and other compounds on varieties of silica has also been studied. Basic dyes are readily adsorbed, to a much greater extent than expected if they formed a monolayer of single molecules. It is suggested that cationic micelles, instead of single ions or molecules, are adsorbed. This is confirmed by a study of spectral absorption curves of solutions of Methylene Blue and pseudo-cyanine chloride before and after treatment with silica. The heat of adsorption of basic dyes is very low and the rates of adsorption are very high. Two acid dyes, viz. Orange I and II, are adsorbed by silica of high specific surface area. The reaction appears to be endothermic and rates of adsorption are very low. The adsorption of Orange I is probably due to hydrogenbonding, and that of Orange II to an ion-exchange or physical process.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: C H Giles
Keywords: Physical chemistry
Date of Award: 1957
Depositing User: Enlighten Team
Unique ID: glathesis:1957-73549
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jun 2019 08:56
Last Modified: 14 Jun 2019 08:56

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