Vapor-Phase Spectra and the Pressure-Temperature Dependence of Long-Chain Carboxylic Acids Studied by a CO Laser and the Photoacoustic Heat-Pipe Detector

Abstract

A resonant photoacoustic heat-pipe (PAHP) cell was constructed and used for spectral studies of four long-chain saturated fatty acids (C10:0 to C16:0) at CO laser wavelengths and temperatures above that of the ambient. Vapor-phase absorption spectra were recorded at temperatures of 383 K for capric acid C₁₀H₂₀O₂, 400 K for lauric acid C₁₂H₂₄O₂, 438 K for myristic acid C₁₄H₂₈O₂, and 445.5 K for palmitic acid C₁₆H₃₂O₂, respectively. In addition, the temperature dependence (298 to 393 K) of vapor pressure was determined for C10:0; measurable PA signals were obtained at a temperature only a few degrees above the melting point for this acid. The data observed for C10:0 could be linearly fitted from as low as 323 K, indicating the validity of the Clausius-Clapeyron equation for temperatures lower than the 398 K < T < 541.4 K range anticipated so far.

Keywords

Vapor pressure Saturated fatty acids Infrared spectrum CO laser Clausius-Clapeyron equation High-temperature photoacoustic cell Heat pipe

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