STUDY OF MUTUAL COMPLEX FORMATION OF ALCOHOLS AND PHENOLS

G. P. NALETOVA

(Presented by Prof. B. V. Tronov, Doctor of Chemical Sciences)

Introduction

The reactions of complex formation of phenols have, in general, been studied fairly thoroughly. Thus, complexes of phenols with amines have been investigated. For example, by the method of thermal analysis, three compounds of pyrocatechol with ethylenediamine were found: 3:1, 2:1, 1:1 [8]; from the maximum of the heat of formation, compounds of o-cresol with pyridine [4] and others were discovered and then isolated in pure form. Complexes of phenols with ketones and aldehydes are known: resorcinol + acetone (1:1)—found by determining vapor pressure [10]; phenol + camphor (1:1, 1:2) [1]; a series of complex compounds with acids [5], with esters, hydrocarbons, and so on is known.

The complex compounds of phenols with alcohols known up to the present time were discovered mainly by two methods: thermal analysis [6] and measurement of vapor elasticity [9, 10]. In our laboratory, complexes of both alcohols and phenols with other organic compounds have been successfully studied by the method of B. V. Tronov and L. P. Kulev [2, 3]. In the present work this method was applied to the study of alcohol–phenol mixtures. All systems were investigated in solutions. Because of the low solubility of hydroquinone, it was not used in this work. In parallel with the electrochemical study, the refractive index was determined. In addition, for a number of systems the temperature rise during reaction with sodium was measured.

Method of Conducting the Investigations

Electrochemical method. The measurements were carried out in the apparatus of B. V. Tronov and L. P. Kulev, where a CIV microvoltmeter with a resistance of 942 ohms was used, manufactured by the Physics Institute at Leningrad University. The electrodes were a platinum crucible and a rod cut from metallic sodium. Those systems in which benzene or xylene was used as the solvent were investigated at a temperature of 20–21.5°. Most of the systems were investigated in ether solution at a temperature of 13–14°. The maximum values of the microvoltmeter needle deflection were plotted on a composition–voltage graph in the form of a curve. Good results have already been obtained by this method in the study of complex formation of alcohols [3] and phenols [2] with other organic compounds. The electrochemical method was also used to check the purity of the alcohols employed.

Refractometric method. This method had already been used in studying the complex formation of phenols with other organic compou...

…with [7] and gave positive results. Most of the systems were studied in ether solution. The measuring instrument used was an Abbe refractometer. The electrochemical studies and the determinations of the refractive index were carried out under identical conditions.

Temperature measurements. The rise in temperature was determined during treatment of an alcohol–phenol mixture with metallic sodium in benzene or xylene solution; the ether solution did not give any appreciable change in temperature. For the measurements a thermometer with a scale division of 0.2°C was used; it was placed in the alcohol–phenol mixture before its treatment with sodium. After a constant temperature had been established, a freshly cut rod of metallic sodium, 10 mm in diameter and 7 mm high, was placed in the mixture. The temperature was measured every minute; the maximum rise in the temperature of the mixture under test was determined. The results obtained were plotted as graphs in the coordinates degrees—composition %.

Detailed results of the study of the phenol—$C_5H_{11}OH$ system are given in Table 1 (a, b, c). The results of all electrochemical and temperature measurements are given in summary Tables 2 and 3, where the molecular ratios of alcohols and phenols corresponding to the maximum on the composition—property curves are presented. For some systems complete composition—property diagrams are given (Figs. 1, 3).

Results of the Refractometric Study

The refractive index was determined for 31 systems. In 5 of them no noticeable deviations from additivity were found. Special points were found in the following systems.

Phenol + trimethylcarbinol.
Phenol + benzyl alcohol.
Phenol + cyclohexanol.
2-naphthol + cyclohexanol.
2-naphthol + isobutyl alcohol.

Dichlorophenol + cyclohexanol.
Pyrocatechol + n-butyl alcohol.
Pyrocatechol + isobutyl alcohol.
Pyrocatechol + cyclohexanol.

In Fig. 2 are presented composition—property diagrams for systems in which the refractive index indicated the strongest interaction.

Table 1a

Study of the phenol—isоamyl alcohol system

Electrodes—sodium–platinum
Solvent—benzene

Concentration 3.33 g-m/l
Temperature 21.0–22.0°C

Fig. 1. Phenol + benzyl alcohol, concentration 3.3 \(\frac{\mathrm{g\!-\!m}}{\mathrm{l}}\), solvent—xylene.

Fig. 2. Refractometric study.

1—phenol + trimethylcarbinol, 3.3 \(\frac{\mathrm{g\!-\!m}}{\mathrm{l}}\), solvent—benzene; 2—phenol + benzyl alcohol, 1.0 \(\frac{\mathrm{g\!-\!m}}{\mathrm{l}}\), solvent—ether; 3—phenol + cyclohexanol, 1.0 \(\frac{\mathrm{g\!-\!m}}{\mathrm{l}}\), solvent—ether.

Fig. 3. Phenol + cyclohexanol, 3.0 \(\frac{\mathrm{g\!-\!m}}{\mathrm{l}}\), solvent—xylene.

Table 1b

Solvent—benzene

Temperature—21.0–22.0°C

Concentration—3.33 g-mol/L

Table 1v

Solvent—benzene

Concentration—3.33 g-mol/L

Table 2

Results of the electrochemical study

(Continuation of Table 2)

Table 3

Results of the temperature study

Discussion of Results

Structure of complexes of alcohols with phenols. As a general comparison of the chemical properties of alcohols and phenols shows, phenols have a more strongly expressed acidic character. Consequently, in the formation of the complex compounds considered in this work, phenols should function as electron acceptors, being attracted by their hydrogen to the unshared pairs of the alcohols. Thus, the structure of complexes of molecular composition 1:1 should correspond to the formula

\[ \mathrm{Ar{-}O{-}H\ldots O{-}Alk} \]
\[ \phantom{\mathrm{Ar{-}O{-}}}\big| \]
\[ \phantom{\mathrm{Ar{-}O{-}}}\mathrm{H} \]

Other ratios can be explained by the participation in complex formation of associated molecules of the alcohol, the phenol, or both together. In this case the degree of association may change owing to the emergence of a complex bond with another component of the system. Thus, if, for example, the alcohol by itself has an association coefficient of 2, then the possibility is not excluded that, in the complex molecule—

\[ \mathrm{Ar{-}O{-}H\ldots O{-}Alk} \]
\[ \phantom{\mathrm{Ar{-}O{-}H\ldots O{-}}}\big| \]
\[ \phantom{\mathrm{Ar{-}O{-}H\ldots O{-}}}\mathrm{H\ldots O{-}Alk} \]
\[ \phantom{\mathrm{Ar{-}O{-}H\ldots O{-}H\ldots O{-}}}\big| \]
\[ \phantom{\mathrm{Ar{-}O{-}H\ldots O{-}H\ldots O{-}}}\mathrm{H} \]

—the free hydrogen will so increase its activity under the influence of the hydrogen of the phenolic hydroxyl that it will be able to attract another alcohol molecule and form a more complex compound.

Influence of the composition and structure of alcohols and phenols on their complex formation. Of the research methods used in this work, only determination of the refractive index directly indicates the strength of interaction of the compounds studied. This method showed that complex formation is most sharply expressed in 9 systems. Complex formation was not detected in 5 systems. In the remaining cases, on the refractive-index–composition curve there was a more or less noticeable deviation from additivity. However, this method is not very sensitive. The most complete results were obtained in the electrochemical measurements, where what is determined is not, in fact, the intensity of the complex-formation process itself, but the activity of the complex already obtained with respect to sodium. These results show, above all, that complexes with methyl alcohol are the most active toward the metal. Complexes

phenols with ethyl alcohol in most cases proved to be less active. Complexes with propyl and isopropyl alcohols gave almost the same increase in voltage, although isopropyl alcohol by itself is considerably inferior in activity to propyl alcohol [3]. Isobutyl alcohol in a complex with phenol is considerably inferior in activity to both propyl alcohols, but is considerably superior to trimethylcarbinol. The latter, however, noticeably surpasses isoamyl alcohol, which also sharply contradicts the results of experiments with these alcohols without the addition of phenol. It may be thought that in secondary and tertiary alcohols complex formation with phenol proceeds more intensively and leads to a higher concentration of complexes in solution, and that the complex has greater reactivity toward sodium than do the components of the complex separately.

The phenolic complexes of cyclohexanol and benzyl alcohol, of which the latter is more active, in terms of their reactivity stand between isobutyl alcohol and trimethylcarbinol. Complex formation of naphthols, dihydroxybenzenes, and chloro derivatives of phenol can be judged from the results of experiments with ethereal solutions. Comparison of the activity of 1- and 2-naphthols in complexes with different alcohols leads to indefinite results. p-Chlorophenol showed considerably greater activity than phenol, but the introduction of a second and third chlorine atom sharply reduces the reactivity. Resorcinol in experiments with methyl alcohol and cyclohexanol did not show any noticeable difference in activity in comparison with phenol. In pyrocatechol, a sharp decrease in activity upon the addition of alcohols was observed, probably due to the formation of an intramolecular hydrogen bond.

Comparison of research methods. The best results in application to the systems studied were shown by the electrochemical method of B. V. Tronov and L. P. Kulev. It made it possible to detect 60 compounds in 31 systems. Eight systems were studied by the temperature method; in them 8 compounds were detected. Of these, 3 compounds fully coincided in composition with the data of the electrochemical method, 3 showed incomplete agreement, and in 1 system a discrepancy was observed. In these same systems, 20 compounds were found by the electrochemical route, of which 14 were not observed by the temperature method. Determination of the refractive index was carried out for 31 alcohol–phenol systems; 5 systems showed no deviations from additivity, while in 9 systems special points were found that corresponded to 16 compounds. By the method of B. V. Tronov and L. P. Kulev, 16 compounds were found in these systems: the composition of 4 compounds coincides completely, and of 4 incompletely. With the aid of the refractive index, at points where the electrochemical method gave neither a maximum nor a minimum, 8 compounds were discovered.

Conclusions

1. Complex formation in 31 alcohol–phenol systems was studied.
2. The investigation was carried out by three methods:
   a) electrochemical (B. V. Tronov and L. P. Kulev);
   b) refractometric;
   c) by measuring the temperature increase.
3. Considerations are presented on the structure of the complexes formed in the systems studied, and on the influence of the nature of the compounds taken on the complex-formation reaction and on the activity of the complexes toward sodium.

References

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