52 4 R. REINMANN UND A. TANNER Beitrag zur Chemie des Galliums The Synthesis and some Properties of Gallium Ethoxide R . R e in m a n n u n d A . T anner Forschungsinstitut der Schweizerischen Aluminium A.G., Neuhausen am Rheinfall/Schweiz (Z. Naturforsdig. 20 b, 524—525 [1965] ; eingegangen am 6. März 1965) Experimental amounts in the range of 50 g each of gallium triethoxide have been prepared by reacting gallium trichloride with freshly prepared sodium ethoxide in absolute alcohol. Chloride, always present in the raw product, can be eliminated by precipitation with silver nitrate. Gallium triethoxide crystallizes in colourless needles, melting at 144.5 °C. The density of the very hygro­ scopic product is 1.23 g/cc. It is volatile at elevated temperature in vacuum. By alcohol interchange, the ethoxide can easily be transformed to the isopropoxide. Although many of the various alkoxides are Sodium metal is carefully freed from its superficial described in the literature, those of gallium were crust in a glove box under dry nitrogen, weighed, and lacking until recently. dissolved in ethanol under reflux. The stoichiometric amount of gallium trichloride, dissolved in cooled etha­ The purpose of this investigation was to find a nol, is added dropwise to the sodium ethoxide solution. suitable method for the preparation of gallium The mixture is finally heated to ebullition for about ethoxide, and to evaluate also some properties of 30 minutes. After cooling, when the NaCl and the the new compound. major part of the Gallium ethoxide are precipitated, benzene is added to about 30 — 40% of the final When writing this manuscript, we came across the mixture. The latter is heated to ebullition, until the publications by R. C. and R. K. M eh r o tra 1, and ethoxide is dissolved again. For the hot filtration from F u n k and P a u l 2 describing briefly the preparation the NaCl at reduced pressure, a closed apparatus of gallium triisopropoxide, and gallium triethoxide which protects the compound from moisture, is used. respectively, not giving many details nor any pro­ The filtrate is distilled at normal pressure until the solid ethoxide appears, which is then dried in a va­ perties of the compounds. cuum. Finally, the raw product is cautiously distilled from a “Kragenkolben” in the vacuum of an oil pump. Experimental Purification. The distilled gallium ethoxide Preparation of materials. Preliminary always contains some chloride, which cannot be re­ tests showed that it is most essential to work only with moved by further distillation or by crystallisation from carefully dried solvents, and with ethanol, absolutely ethanol/benzene mixtures. free from benzene (see also later). This chloride can be eliminated by addition of an alcoholic AgN03 solution to the dissolved ethoxide, Gallium trichloride was prepared by reacting the metal which is then filtered from the precipitated AgCl. with dry HCl-gas, as widely described in the litera­ ture. Purification was made by double distillation in Analyses. Since the ethoxide is very sensitive to HCl-gas, and in N2 . moist air, samples for C-, H- (5 —10 mg each), and for Sodium was the “pro Analysi” quality of Merck, Darm­ ethoxyl (40 — 50 mg each) determinations are directly stadt, Germany. distilled in weighed, small tubes, which can be sealed Ethanol. Benzene-free ethanol was refluxed with Mg- off. chips during 8 hours, according to L u n d and B j e r - Found Found r u m 3, and then distilled. The remaining water con­ (not purified) (purified Calcd. tent was 0.003% (Karl Fischer - titration). % samples) % % Benzene was refluxed with Na during 3 hours, and then distilled. Remaining water 0.01 per cent. -C 34.75; 35.01; 34.95 34.83; 34.61 35.18 Isopropanol was dried with K2C03 for 24 hours, and -H 6.81; 7.23; 6.95 7.07; 7.12 7.38 distilled over Ca. Remaining water 0.18 per cent. -O C 2H5* 68.3; 67.8 66.8; 67.3 66.0 Cl < 0.1 Apparatus and Procedure. Gallium tri­ ethoxide is prepared in the following way : * samples hydrolysed and ethanol oxydised with KMn0 4 . 1 R. C. and R. K. M e h r o t r a , Current Sei. [India] 33, 241 3 H. L u n d and J. B j e r r u m , Ber. dtsch. chem. Ges. 64, 210 [1964]. [1931], 2 H. F u n k and A. P a u l , Z. anorgan. allg. Chem. 330,70 [1964]. BEITRAG ZUR CHEMIE DES GALLIUMS 5 2 5 Properties of gallium triethoxide. practical in the synthesis of the aluminium com­ Colourless needles, volatile at elevated temperature. pound, the reaction of gallium trialkyl with ethanol Thermal decomposition from about 200 °C. Melting and others gave no positive results. Only the reac­ point: 144.5 °C. Density (solid): 1.23 g/cm3. Very soluble in benzene and in boiling ethanol; slightly tion of sodium ethoxide with gallium trichloride, soluble in cold ethanol and in hydrocarbons. both in ethanol, according to an old principle of Gallium triisopropoxide. The isoprop- G r i m a u x 5’ 6, gave us the ethoxide with a good yield. oxide is easily obtained from the ethoxide by alcohol 3 NaOC2H5 + GaCl3 -> Ga (OC2H5) 3 + 3 N aC l. interchange reaction. Ga (OC2H5) 3 + 3 C3H7OH -► Ga (OC3H7) 3 + 3 C2H5OH. Stoichiometric amounts of the starting materials are necessary, because of the formation of alkoxide salt, The ethoxide is refluxed with excess isopropanol for very soluble in ethanol 2 hours. The alcohol is then distilled off at normal pressure, and the residue distilled in vacuum. The Ga (OC2H5) 3 + NaOC2H5 ^ N a[G a (OC2H5) 4] . isopropoxide crystallises very slowly in colourless needles. The melting point could therefore only be On the other hand, excess GaCl3 is difficult to determined very approximately to be at about 60 °C. remove, because of its “organic” behaviour. The vapor pressure is: 0.15 mm Hg at 109.5 °C, It is most essential to use benzene-free ethanol and 0.52 mm Hg at 123.0 °C 4. for the primary reaction, benzene and ethanol being This corresponds well with the indication of M e h r o - subject to Friedel Crafts reaction in the pre­ t r a *. Analyses of gallium triisopropoxide sence of GaCl3 . Found % Calcd. % Excess AgN03 must be strictly avoided in purifi­ cation, for its catalytic effect on the decomposition -C 43.18; 43.72 43.76 -H 8.10; 8.47 8.58 of the compound when distilling. For the same -OC3H7 71.24; 71.53 71.76 reason the bath temperature should not be raised above 190 °C. The described reaction has been made with Discussion amounts up to 60 grams of GaCl3, corresponding In preliminary tests we tried various methods for to approx. 50 g of the purified gallium triethoxide, the preparation of the ethoxide, but without success. the yield being about 70 per cent. Losses are mainly The direct reaction of the metal with ethanol, very due to hydrolysis. 4 H. Lux, „Anorgan.-chem. Experimentierkunst“, J. A. Barth- 5 E. G r im a u x , C. R. hebd. Seances Acad. Sei. 98, 105 [1884]. Verlag, Leipzig 1959, p. 623. 6 P. A. T h ie s s e n and O. K o e r n e r , Z. anorgan. allg. Chem. 180, 65 [1929],.