Sur le Polymorphisme du barbital et le systeme eau-barbital

Abstract

The crystal structures of three forms (I, II and IV) of barbital are well known. The DTA curve of barbital 1 is marked by only one endotherm, at 186 ~ which is the melting point of this crystalline form. For barbital II, the DTA curve shows a first endotherm at 160 ~ which indicates the transition point II ~ I, and then an endotherm at 186 ~ for the melting of form I. By fast cooling of a boiling saturated aqueous solution, another crystalline form of barbital (form X) can be obtained. The DTA curve of this new sample shows another endotherm, at 119 ~ preceding the endotherms at 160 and 186 ~ Though the TG curve does not indicate any weight loss at this temperature, this endotherm does not indicate a new phase transition, but a monotectic equilibrium.This monotectic equilibrium (XLL = 78 mol % H20, XL2 = 98 tool % H20 ) is observed at 1197 in the phase diagrams (isochoric sections at V/m = 7 cm3.g -1) of the water--barbital systems established for form I, form II and form X.Le barbital CsH 12N203 (di6thyl-5,5' 1 H, 3H, 5H-pytimidine trione-2,4,6, masse molaire M = 184,2) est utilis6 en th6rapeutique pour ses propri&6s hypnotiques d6couvertes en 1903 par Fischer et Von Meting.Son polymorphisme a fait l'objet de nombreuses &udes. Kofler [1, 2] a caractdris6 quatre formes cristallines sur la base de la morphologie des cristaux, de letirs points de fusion et des donn6es de diffraction des rayons X des poudres cristaUines. Ces r6sultats ont 6t6 confirm6s par Huang [3] qui pr6cise les distances r&iculaires.

Liquid-Liquid Miscibility Gaps and Hydrate Formation in Drug-Water Binary Systems: Pressure-Temperature Phase Diagram of Lidocaine and Pressure-Temperature-Composition Phase Diagram of the Lidocaine-Water System

“…Surprisingly, to the best of our knowledge, the ability of lidocaine to form “nonconventional” emulsions has never been related to the formation of miscibility gaps, that can easily be evidenced by visual observation of how lidocaine–water mixtures behave on heating in screw‐cap tubes. Miscibility gaps have already been observed in other drug–water systems (systems barbital–water16 and phenobarbital–water,17 for instance). Nevertheless, up to what extend such miscibility gaps form in drug–water systems remains to be assessed through systematic investigations.…”

Le systeme EAU-phenobarbital

“…Nous avons vu dans un pr6c6dent article [1] que l'hydrate du barbital n'6tait pas connu et qu'il n'avait pu &re mis en 6vidence par l'&ude polythermique h volume constant du systbme eau-barbital. En revanche, l'hydrate du ph6nobarbital a &6 d~crit ; il poss~de une fusion incongruente et Sa structure cristalline est r6solue [2].…”