Zinc chloride-methanol melt

High-Yield Coal Conversion in a Zinc Chloride Methanol Melt Under Moderate Conditions... 

The BASF route started from hydroquinone, which was converted to 2,5-dihydroterephthalic acid by a Kolbe-Schmitt reaction. One mole of this acid was treated with two moles of an arylamine, both components being in the form of a suspension in aqueous methanol. This was added to a small amount of a solution of vanadium(III) chloride and sodium chlorate. Gentle heating gave a 95% yield of 2,5-bis(arylamino)benzo-l,4-quinone-3,6-dicarboxylic acid. Ring closure to the trans-quinacridonequinone took place in the presence of concentrated sulphuric acid at 60-80 °C. This was then reduced to the required crude pigment by zinc or aluminium powder in caustic soda under pressure,in an aluminium chloride/urea melt or by the use of a sulphuric acid/polyphosphoric acid mixture. 

A solution of 300 g. (3.22 moles) of aniline in 400 ml. of water and 1 1. of concentrated hydrochloric acid is diazotized by the addition at 0-10° of a solution of 220 g. (3.20 moles) of sodium nitrite in 250 ml. of water. The mixture is held at 0° and stirred while a solution of 280 g. (2.05 moles) of zinc chloride in 120 ml. of dilute hydrochloric acid is added slowly. The precipitated salt (90 yield) is filtered off by suction, pressed free of water, and washed with dry acetone (500 ml.) until free of all moisture. A mixture of 600 g. of the dry zinc salt, 1.5 1. of dry acetone, and 180 g. (1.0 mole) of arsenic trichloride (Caution—toxic substance) is stirred vigorously and held below 5° while 220 g. of zinc dust is added in small portions over a 2-hour period. The mixture is heated under reflux for 15 minutes and filtered, and the filtrate is evaporated on a water bath. The residual oil is stirred with 200 ml. of dilute hydrochloric acid, and the solid product (300 g.) is removed by filtration. This crude triphenylarsine is converted to the pure material (m.p. 60°) by melting it under an equal weight of methanol, cooling, and collecting the residual crystalline solid. 

In contrast to sulfur poisoning, ZnO gives no protection against chloride compounds. Zinc oxide reacts to form Zn chloride, which also has a low melting point and cause further poisoning and sintering problems. Chloride compounds in the feedstock can be reduced by guard beds of either alkalized alumina or extra, sacrificial catalyst. Today catalyst deactivation caused by poison (sulfur and chlorine) is rarely a problem in methanol synthesis, because poisonous compounds are effectively removed in the feedstock pretreatments. 

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