Ginger, black pepper, and chili powder were extracted using near-critical carbon dioxide, propane, and dimethyl ether on a laboratory scale to determine the overall yield and extraction efficiency for selected pungent components. The temperature dependency of extraction yield and efficiency was also determined for black pepper and chili using propane and dimethyl ether. The pungency of the extracts was determined by using an NMR technique developed for this work. The volatiles contents of ginger and black pepper extracts were also determined. Extraction of all spice types was carried out with acetone to compare overall yields. Subcritical dimethyl ether was as effective at extracting the pungent principles from the spices as supercritical carbon dioxide, although a substantial amount of water was also extracted. Subcritical propane was the least effective solvent. All solvents quantitatively extracted the gingerols from ginger. The yields of capsaicins obtained by supercritical CO(2) and dimethyl ether were similar and approximately double that extracted by propane. The yield of piperines obtained by propane extraction of black pepper was low at approximately 10% of that achieved with dimethyl ether and CO(2), but improved with increasing extraction temperature.

The large kinetic solvent isotope effects for the neutral hydrolysis of acetic and propionic anhydride show unusual temperature dependency; the former passing through a maximum at about ISo, the latter showing a minimum at 30". This unusual temperature dependency is the consequence of widely different values of the apparent ACp* in H 2 0 and D 2 0 : the value for acetic anhydride in H,O being -74 f 2 cal deg-' mol-' but -32 + 4 in D 2 0 . The corresponding values for propionic anhydride being -31 + 2 in H 2 0 but -94 f 10 in D20. The implications of these differences are discussed.L'importance des effets isotopiques cinktiques dans l'hydrolyse en milieu neutre d'anhydride acetique et propionique depend Ctrangement de la temperature; le premier passe par un maximum a environ 15" tandis que le dernier presente un minimum a 30". Cette dependance inhabituelle par rapport a la temperature est la conskquence des valeurs tres differentes du ACp* apparent dans H 2 0 et D 2 0 : la valeur pour l'anhydride acetique dans H 2 0 etant de -74 t 2 cal deg-' mol-' mais de -32 + 2 dans D20.Les valeurs correspondantes pour I'anhydride propionique sont de -31 k 2 dans H 2 0 mais -94 f 10 dans D 2 0 . Les consequences de ces differences sont discutees. Canadian Journal of Chemistry, 49, 3665 (1971) IntroductionThe spontaneous hydrolysis of carboxylic acid anhydrides have been widely studied (1-10). The reaction is characterized by large kinetic solvent isotope effects (k.s.i.e. = kHZo/kD2,) and large negative entropies of activation (AS*). Such results were interpreted as being consistent with the requirements of a general base catalyzed mechanism, BAc2, and were taken to imply (1 1) that more than one water molecule was tightly constrained in the transition state. Our interest in the effect of temperature on solvolytic rates led initially to an investigation of the temperature dependency of the large kinetic solvent isotope effect for acetic anhydride.The experimental problem simply required that we extend the careful investigation of Gold (5) over a wide temperature range and obtain a complementary set of rate data in D,O. The results were so surprising that we were led to extend our investigation to study the hydrolysis of propionic anhydride and to other anhydrides. In this paper we report our findings for the hydrolysis of acetic and propionic anhydride.

In a one-pot synthesis at room temperature the N-methylpyridazinium ion (1) dimerizes stereospecifically and with 100 % conversion in a series of OH -catalyzed processes to give a new tetraazafluorene (2). Four of the individual steps can be identified directly and monitored by H NMR spectroscopy.

The temperature dependence of the rate of hydrolysis of α-bromoisobutyrate ion in water was determined over a temperature range 9–37 °C. From these data corresponding values of ΔH≠, ΔS≠, and ΔCP≠ have been derived. The implication of these terms, together with corresponding data for hydrolysis in D2O and for the secondary deuterium isotope effect from the hydrolysis of (CD3)2CBrCOO−, provide a basis for reexamining the detailed mechanism with particular reference to accompanying solvent reorganization.

In einer Eintopfsynthese bei Raumtemperatur dimerisiert das N‐Methylpyridazinium‐Ion 1 in einer Folge von OH−‐katalysierten Prozessen stereospezifisch und mit 100% Umsatz zum neuen Tetraazafluoren 2. Vier der Einzelschritte lassen sich 1H‐NMR‐spektroskopisch direkt nachweisen und verfolgen.