Decarboxylation in the synthesis of 4‐alkyl‐, 4‐alkenyl‐ and 4‐acylpyrimidines

Decarboxylation of allylic esters of 4‐carboxypyrimidines in toluene at 111 °C in the presence of a Pd(0) catalyst, gives a mixture of a 4‐alkenylpyrimidine and a pyrimidine unsubstituted in the 4‐position. If the decarboxylation is carried out in the presence of benzaldehyde, then benzaldehyde is added to the 4‐position. Decarboxylation of 4‐carboxypyrimidines in the presence of different electrophiles, results in incorporation of the electrophile into the 4‐position together with a pyrimidine unsubstituted in the 4‐position. Use of microwave irradiation enhances the rate of the decarboxylations.     

Calorimetric Investigations of Some Phases in the System Sodium Fluoride - Aluminium Fluoride

Beside the two well-known minerals cryolite, Na₃AlF₆, and chiolite, Na₅Al₃F₁₄, the binary system NaF-AlF₃ also contains a third compound, NaAlF₄, sodium tetrafluoroaluminate. Solid NaAlF₄ has been prepared from its vapour under controlled conditions. The stability of NaAlF₄ has been investigated by differential scanning calorimetry. It is shown that the disproportionation of the compound: 5NaAlF_4(s)=Na₅Al₃F_14(s)+2AlF_3(s) takes place at considerable rate between 700 and 900 K. The enthalpy of this reaction is calculated and found to be -66.9 kJ. Enthalpies of the two solid state transitions α-Na₃AlF₆ → β-Na₃AlF₆ and α-AlF₃ → β-AlF₃ have also been measured and new values are reported. The enthalpy of formation of chiolite, Na₅Al₃F₁₄, at 900 K has been recalculated from enthalpy increment data obtained by drop calorimetry. A value of ΔH₉₀₀ ^o = -7513.6±12.0 kJ mol^-1 has been obtained. This value is in disagreement with the recommended value given in JANAF Thermochemical Tables given at 900 K ΔH_f ^o = -7559.2 kJ mol^-1. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ein neues Randwinkel-Meßgerät und die Bedeutung des Randwinkels bei technischen Verfahren

Ohne Zusammenfassung