NMR Study of the ROH‐D₂O Systems I. Ethanol, Propanol‐1, Propanol‐2

Abstract

The NMR spectra of mixtures of ethanol, propanol-1, and propanol-2 with heavy water are discussed. The intensities of the hydroxyl and water signals have been found to agree with the theoretical probability curves. No coalescence of these signals could be found up to molar fraction of D,O equal to 0.9. The spectra of ROH-D,O systems are shown to be more representative of water-alcohol mixtures than are those of ROH-H,O systems. Die KMR-Spektren von Mischungen von Xthanol, Propanol-1 und Propanol-2 mit schwerem Wasser werden diskutiert. Es wird gefunden, daB die Intensitaten der Hydroxyl-und der Wassersignale mit den theoretisch zu erwartenden Hiufigkeiten im Einklang stehen. Bis zu D,O-Molenbriichen von 0,9 fallen diese Signale nicht zusammen. Es wird gezeigt, da13 die Spektren der ROH-D,O-Systeme mehr AufschluB uber Wasser-Alkohol-Mischungen geben als die der ROH-H,O-Systeme. Introdrrction Addition of small amounts of acid or base to ethanol increases the rate of exchange of hydroxyl protons, i. e. of the reaction + EtOH &OH + EtOir which decouples them from methylene protons and, as a consequence, simplifies the NMR spectrum of the alcohol [8]. This phenomenon can be examined quantitatively by using McConnell's treatment [9] of the Bloch equations [14]; the values of the mean life-time between exchange events has been estimated by advanced approach [1, lo]. The same results have been obtained by adding buffers to EtOH [4].The addition of an inert solvent, on the other hand, decreases the degree of association of ethanol molecules and causes a shift of the OH signal into a higher field [2, 31. The influence of heat combines these two effects[13] since the increase of temperature favours both the proton exchange and dissociation. These results can be applied also to other simple alcohols [2, 5, 81.Water, when added to ethanol, acts in the same wayboth as an exchange accelerator and a diluent. Its accelerating action is based on reactionEtOA + HOH F? EtOH + HOk.Here, in addition, the coalescence of OH and H,O signals has been found at about 50 mole-% H,O when its concentration is varied from 0 to 100% [17]. The same phenomenon has been observed when acid has been added [6] or temperature increased 1151 in a water-ethanol mixture, indicating the increase of the rate of exchange of hydroxyl protons. These investigations have also been extended to other simple alcohols [8, 11, 121. So far, all papers deal with mixtures of alcohols and ordinary water. The strong H,O signal, however, makes the observation of alcohol signals difficult, particularly in samples with high water concentration. We have, therefore, determined to examine the NMR spectra of mixtures of heavy water and simple alcohols. The latter have included ethanol, propanol-1, and propanol-2. Methanol has been omitted from this series owing to its extreme rate of exchange [8] which makes it susceptible to the least amount of impurities. A qualitative treatment of such systems is given in this paper. ExperimentalHeavy water used was that of the Isotopes Spe...