Excess heat capacities of mixtures of two alcohols

Abstract

The molar excess heat capacity ( C i ) has been obtained through the concentration range at 25°C for mixtures of alkan-1-01s: methanol with butanol, hexanol and decanol and decanol with butanol and hexanol. C i is negative and small, increasing in magnitude with difference in chain length of the alkan-1-01s to a maximum of -3 J mol-' K-' for methanol-decanol. C i has also been measured at 25°C for methanol and other alkanols mixed with iso-, sec-and tert-butyl alcohol (I), 2-methylbutan-2-01 (ll), 3-methylpentan-3-01 (111) and 3-ethyl-pentan-3-01 (IV). With increasing steric crowding of the tertiary OH, CF becomes extremely large, -18 J mol-' K-' for methanol-lV at equimolar concentration, the apparent molar C, of methanol in IV being negative at low concentration. The negative CE(x) for methanol-l is of normal positive curvature, but with II, CE has a W-shaped concentration dependence exhibiting two regions of positive Ci(x) curvature separated by a region of negative curvature. An extension of the Treszczanowicz-Kehiaian association model has been made to alcohol-alcohol mixtures with consideration of multimers mainly confined to linear tetramers. Assuming equal enthalpies and equilibrium constants for H-bonding between like alkan-1-01s (AA and BB) and between unlike alkanols (AB) leads to positive C; predictions. The experimental negative CF values are associated with a lowering of the equilibrium constant for H-bond formation in the alkan-1-01 with increasing chain length coupled with relatively stronger AB bonding. The equilibrium constant, K,, , for H-bonding between tertiary alcohol hydroxyls is found to be lowered by steric crowding of the tertiary hydroxyl, raising the C, of the pure liquid. The constant, K,, , for bonding between primary (A) and tertiary (B) hydroxyls in the multimer chain is less affected by the tertiary crowding resulting in lower solution C, and large negative C i . The S-and W-shape concentration dependences require modifications of KA, owing to the proximity in the tetramer chain of either A or B alcohols resulting in an effective concentration dependence of KA, .

Excess molar heat capacities for (1-butanol+1,3-butanediol) at temperatures from (285 to 353) K

“…Simultaneously, the minimum values of the C E p;m are correlated with the magnitude of the C p,m values of the pure butanols and the minima are in the order: 1-butanol < i-butanol < s-butanol < t-butanol [9]. Moreover, the negative values of C E p;m have been also found to exist for the other (1-alkanol + 1-alkanol) systems [7,8]. It must be pointed out here, that (1-alkanol + tertiary alcohols) systems show generally considerably more complicated composition dependence of C E p;m , i.e., s-shaped or w-shaped [8,10].…”

“…In this case, the equimolar value is ca. 0.4 J AE K À1 AE mol À1 [8]. It is also interesting to note that the C E p;m values for the four systems of (methanol + isomeric butanol) are negative and show a simple concentration dependence.…”

“…It must be pointed out here, that (1-alkanol + tertiary alcohols) systems show generally considerably more complicated composition dependence of C E p;m , i.e., s-shaped or w-shaped [8,10]. In addition, with increasing steric crowding of the tertiary OH, C E p;m becomes extremely large, e.g., À18 J AE K À1 AE mol À1 for (methanol + 3-ethyl-3-pentanol) at equimolar concentration [8].…”

Molar heat capacities for (1-butanol+1,4-butanediol, 2,3-butanediol, 1,2-butanediol, and 2-methyl-2,4-pentanediol) as function of temperature

“…In these cases, the equimolar values are À1.41 J AE K À1 AE mol À1 and ca. À0.4 J AE K À1 AE mol À1 , respectively [26,27]. It is also interesting to note that C E p;m values for the all four systems of (methanol + isomeric butanol) are negative and show a simple concentration dependence.…”

Excited State Proton Transfer Reaction of 4-Methyl-2,6-dicarbomethoxyphenol in Some Protic Solvents at Room Temperature and 77K: Interaction with Base

“…Accordingly, these higher alcohols cannot accept proton from CMOH. Yao et al made similar suggestions (25). It is suggested that with increasing steric crowding in the neighborhood of the hydroxyl group, hydrogen bonding interaction will be substantially weakened.…”