Chemistry of inorganic compounds – Carbon or compound thereof – Oxygen containing
Patent
1981-11-23
1984-03-20
Straub, Gary P.
Chemistry of inorganic compounds
Carbon or compound thereof
Oxygen containing
C01F 700, A61K 3306, A61K 3308, A61K 3310
Patent
active
044380852
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to dihydroxyaluminum sodium carbonate and provides an improved method for its manufacture. In this specification, the abbreviation "DASC" will be used for "dihydroxyaluminium sodium carbonate".
DASC is probably the most widely used gastric antacid in the world. It has the formula (HO).sub.2 AlOCO.sub.2 Na and is usually prepared by a batch process in which aluminium isopropylate (i.e. aluminium triisopropoxide) is contacted with sodium bicarbonate in water (see U.S. Pat. No. 2,783,179). Other methods of manufacture are known. In particular, Japanese Patent Application No. 38318/1972 discloses a process which can be operated continuously and in which an aluminium salt is contacted with sodium carbonate in water at a pH maintained in the range 7.2 to 10.5 by addition of sodium hydroxide and, if necessary, carbon dioxide.
The specification of Japanese Patent Application No. 38318/1972 states that the aluminium salt and sodium carbonate can be added in equal parts but that it is preferable to use an excess of sodium carbonate to provide more than two moles CO.sub.2 per mole Al.sub.2 O.sub.3. The Examples provided in the specification use essentially stoichiometric amounts of aluminium salt and sodium carbonate. In particular, Examples 1 and 3 use an Al.sub.2 O.sub.3 :CO.sub.2 mole ratio of 1:2 and in Example 2 said mole ratio is 1:4. The only claim of the Japanese application specifies aluminium chloride as the aluminium salt but aluminium sulphate, aluminium nitrate, aluminium acetate, alum and aluminium hydroxide are stated in the specification to be suitable aluminium salts. There is no exemplification of the use of aluminium chloride as the aluminium salt and the only Examples in the specification exemplify the use of aluminium sulphate and aluminium hydroxide as the aluminium salt. When the procedures reported in Examples 1 and 2 were repeated by us with the only differences being that aluminum chloride was used instead of aluminium sulphate and the reaction was carried out on a smaller scale, substantially no DASC was obtained by the procedure of Example 1 and only low purity DASC was obtained by the procedure of Example 2. When Example 3 was repeated by us using a commercial grade aluminium hydroxide, no DASC was obtained.
The process of Japanese Patent Application No. 38318/1972 had the advantages over the usual process of manufacturing DASC from aluminium isopropylate that relatively inexpensive inorganic aluminium salts can be used and that it is capable of continuous operation. It appears that the Japanese process has not been operated commercially.
It will be appreciated from the above that, whilst Japanese Patent Application No. 38318/1972 teaches a new and potentially useful process of obtaining DASC from aluminium salts and sodium carbonate, the process parameters taught are not sufficient for the process to be used on a commercial scale or to obtain high purity DASC. It is an object of the present invention to modify and improve this process to obtain high purity DASC on a commercial scale.
It has now been found that DASC can be obtained in good yield and relatively high purity by contacting an ionic aluminium salt, especially aluminium chloride with an amount of sodium carbonate substantially in excess of the stoichiometric amount. Further, process parameters have been developed which cause the sodium salt by-product produced to be precipitated with the DASC thereby facilitating recycling of sodium carbonate.
According to a first aspect of the present invention, there is provided a method of preparing dihydroxyaluminium sodium carbonate which comprises contacting an ionic aluminium salt with a stoichiometric excess of sodium carbonate in aqueous medium in the presence of sodium hydroxide at a pH in the range 7.2 to 10.5 wherein at least ten parts by weight of sodium carbonate are used per part by weight of the aluminium salt.
According to a second aspect of the present invention, there is provided a method of preparing dihydroxyaluminium sodium carbonate which com
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Jackson et al., Synthesis and Characterization of Dawsonite, Bureau of Mines Report of Investigation 7664, 1972.
Nicholas Proprietary Limited
Straub Gary P.
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