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The reduction of titanium tetrachloride by sodium dispersed on alumina
Notes
153
The accelerated reduction of Np(VI) in chloride media in the presence of platinum that was observed by earlier workers ~s~was confirmed by us. The potential of the couple Pt + 6 C 1 - ~ - P t C l s s- + 2e is - 0 - 7 3 V c8~ which is sufficiently positive for reduction of Np(V1) to the (V) and (IV) states. An analysis by emission spectroscopy of a solution resulting from the addition of a piece of Pt wire to a Np(VI) solution in HCI, showed the presence of platinum in solution. The absorption spectrum of this solution showed that some Np(IV) was present in addition to Np(V) and a large absorption peak occurred in the U.V. at 262-5 m/~; PtCIrt-(aq) is reported to have an absorption maximum at 262 m/~.cs' As a further test on the mechanism of reduction in the presence of platinum, a piece of carefully cleaned platinum wire was weighed on a micro balance and then placed in contact with a 2" 15 × 10 -t M Np(VI) solution in 2 M HCI. After one week the platinum was removed, washed and reweighed; the concentrations of Np(V) and Np(IV) in the solution were determined spectrophotometrically as 1.80 × 10 -3 M Np(V) and 0.30 × 10-aM Np0V). Asimple calculation shows that 2.81 mg of Pt would be required for this reduction. The loss of weight of the Pt wire was measured to be 2-77 rag. This agreement is well within the experimental errors. It would be of interest to repeat these observations using gold metal. It is therefore concluded that the reduction in the presence of Pt is not due to catalysis of the CI- reduction but to reduction by platinum itself. There is no evidence from our work that reduction of Np(VI) by chloride takes place to any significant extent, either in the presence or absence of platinum. DONALD Corms Chemistry Division BRIAN TAYLOR~ Argonne National Laboratory Argonne, Illinois ~ Present address, Chemistry Division, AERE, Harwell, England. ts~ j. j. KIRKLANDand J. H. YoE, Anal. Chim. Acta. 9, 441 (1953).
The reduction of titanium tetrachloride by sodium dispersed on alumina (Received 24 May 1961 ; in revised form 17 July 1961) IT IS known that TiCI4 can be reduced to metallic Ti by the action of sodium, tl~ To obtain a highly active product it has been recommended to use a sodium dispersion prepared by impregnating alumina or sodium chloride with molten sodium, c2~ Indeed, on reacting liquid TiCI, with such a dispersion, a black product was obtained. It is specifically stated that the reaction temperature should be held between 125-200°C. When this precaution was not taken, ignition occurred, the reaction being highly exothermic. On using a lithium dispersion instead of a sodium dispersion violet TiCls was obtained. It is surprising that the relatively small difference in the net electronegativity of Na and Li should cause the reduction of Ti ~v by three additional oxidation states. Indeed, very early, ~3) doubts were raised whether the reduction product obtained under relatively mild conditions was not TiCIt rather than Ti. Since the product from the reaction of TiCI4 with finely dispersed Na shows catalytic properties, it has been thought necessary to check its identity. The analysis of the mixture, which in addition to alumina possibly contains Ti °, TiCI2, Na and NaCI, is not straightforward. It is however possible to distinguish between TiCI, 4- 2Na and Ti ° by first decomposing the TiCI~ and Na with hot NaOH solution. Any metallic Ti present will not react. ~ Both TiCI2 and TiCla will be oxidized to Ti Iv under evolution of hydrogen. ~j The metallic ~1~F. C. ROBINSONand C. C. HUTCHINS,J. Amer. Chem. Soc. 6, 74(1884). M. A. HUNTER,J. Amer. Chem. Soc. 32, 330 (1910). D. LEvy and L. HAMBURGER,Z. Anorg. Chem. 87, 209 (1914). tz~ High Surface Sodium, National Distillers Chemical Co. Ashtabula, Ohio, 1953. is~ O.V.D. PFORDTEN, Ann. Phys. 237, 201 (1887). ~4~ L. WEISSand H. KAISER, Z. Anorg. Chem. 65, 345 (1910). i5l EBELMAN,Ann. chim. phys. 20, 385 (1847).
154
Notes
Ti can then be determined by dissolving it in hot hydrochloric acid, measuring the amount of hydrogen evolved and titrating the Ti m with Fern. ~6) This method is complicated by the fact that some of the nascent hydrogen reduces Ti iv formed in the primary decomposition with NaOH, thereby increasing the amount of Ti m and decreasing the amount of hydrogen evolved.'7) Preparation o f the Reduction Product
Alumina ( " A L C O A " grade F-10) was first crushed to pass 120 mesh and then heated for 3 hr at 500°C in a muffle furnace. It was then transferred to the reaction vessel and kept for a further six hours in vacuo at 450°C. It was then allowed to cool to 150°C and mixed with molten sodium. The mixture was stirred in vacuo for about 15 min and a greyish black dispersion was obtained. The dispersion was allowed to cool and TiCI4 was injected through a rubber gasket using a hypodermic syringe. The dispersion was stirred vigorously both during the addition of the TiCI~ and while the mixture cooled. The colour of the dispersion changed to jet black. The dispersion thus obtained could be filled into separate ampoules for testing and analysing or all of the dispersion could be used. Analysis o f the Reduction Product
The black reduction product was decomposed by the addition of 10 ml of ca. 40 per cent aqueous NaOH solution in vacuo. The solution was heated for about 30 min. Under these conditions both TiCI2 and TiCI3 are oxidized to Ti Iv liberating a corresponding amount of hydrogen. Any residual Na is also decomposed. Only metallic titanium is not attacked. The vessel was then cooled by immersion in liquid air and all the gases were pumped off. The vessel was allowed to warm to room temperature and concentrated hydrochloric acid was added in excess. On heating, the metallic titanium dissolved evolving hydrogen and leaving the titanium in the trivalent state. The vessel was then cooled again in liquid air and the amount of hydrogen evolved was measured. The vacuum was then broken and the Ti II! was rapidly titrated with Fe II1 using NH~CNS as an indicator. If a is the number of moles of hydrogen evolved by the action of HCI and b is the number of 2a+b moles of Ti m titrated, then the quantity of metallic titanium originally present is c -4 gmatoms. The method was checked by analysing a synthetic mixture containing 0.64-gm-atoms Ti ° (crushed sponge Ti metal "B.D.H." laboratory reagent), 0.97 mmoleTiCl2 and 40 gin-atoms Na by the method outlined above. The results were: a = 0.67; b -- 1'15; thence c = 0.62 gm-atoms TiL The results are shown in the Table. It will be seen that the highest percentage of Ti ° found was 8'8%. Obviously most of the TiCI~ was not reduced below TiCI2. TABLE Used
Received
AltOs (ml)
Na (rag-atom)
TiCI4 (mmole)
Na:TiCI~
Ti ° (mg-atom)
Ti°:Ti
15 15 15 15 15 7.5 7.5 7.5
90 90 90 90 90 45 45 45
4.5 9'0 18'0 22'5 36-0 9"0 13.5 27
20 I0 5 4 2'5 5 3-33 l "67
0.11 0.26 0-23 0.33 0-66 0-79 0.69 0.72
2'4 2.9 1.3 1.5 1-8 8"8 5'1 2"7
(6) E. KNECHT and E. HIBBERT,Ber. dtsch. Chem. Ges. 36, 1549 (1903). (~) G. PATSCHEKEand W. SC~ALLER,Z. Anorg. Chem. 235, 257 (1938).
Notes
155
Actually the success of the reduction to Ti ° depends on the temperature reached, which is not uniform. The appearance of a flame shows that at least locally temperatures above 500°C were reached. This is also borne out by the observed sublimation of a little violet TiCI~. Stirring during the injection was not sufficient to result in uniform temperature and the surface of the mass was hotter than the bulk. Therefore a comparison of the results at the same ratio Na:TiC1, shows consistently higher yields of Ti ° when smaller quantities were used. If the reaction is carried out under mild conditions, the temperature being kept below 200°C, no metallic Ti was formed. To verify the effect of temperature a dispersion prepared in the usual way was divided into two parts; the first was analysed without further treatment and the other heated for 3 hr at about 500°C. On heating the yield of Ti ° had risen from 1"5 per cent to 5.1 per cent. It is quite possible that the Ti ° is not formed through the reduction by Na but by decomposition of TiCk. SCWOMS and Stml)STROMcs~ obtained 5 per cent decomposition when TiCIj was heated in vacuo to 475°C. It follows that ordinarily even finely divided Na does not reduce TiCI, below TiClv
Petrochemical Laboratory of the National Council for Research and Development and of the Physical Chemistry Department Hebrew University, Jerusalem
C. EDEN H. FEILCHENFELD D. ZEHAVX
~' W. C. SCHUMBand R. F. SUNDSTROM,J. Amer. Chem. Soc. 55, 596 (1933).
The product of reaction of BF 3 with BzO3* THE FORMATION of trifluoroboroxine, (BOF)s, was first reported by BAUMGARTENand BRims '1,2,s'. The material was reported as a product of reaction of BFs with a number of oxides including BtOs and SiO~. Recently a report suggests that trifluoroboroxine is stable only below - 1 3 0 ° and decomposes rapidly above this temperature to give BFs and B203 '',s~. This leads us to feel that a report of our experiments and observations on the product (hereafter written as product) of the BFs-B=Os reaction is warranted. Boron trifluoride was allowed to react with BzOs and SiO2 in a flow system at 450 ° in the manner outlined in Ref. 1. The white solid product, collected in a cool portion of the system at room temperature, was used in further studies. The product was stable for days at room temperature but melted at about 80 ° with decomposition to B20 8 and BFs. As found by BAUMGARTENand BRLrNS, the material contained B, O and F, but always more BzO t than BFs. A typical analysis showed the ratio of BtOa to BEt to be 2"19. An attempt was made to measure the equilibrium constant between BFs and the tacky mixture of B~Os and product at 80 °. However, the reverse reaction, B2Os(s) + B F , ~ product was very slow at 80 ° and the results were not completely definitive. The heat of formation of the product was determined by measuring its heat of solution in both water and CHnOH after correcting for the heat of solution of the excess B~Os. Assuming that the product was trifluoroboroxine, the entropy of the material was calculated. The following table gives a summary of the properties observed, calculated and estimated for (BOF)s. Until a definite proof of the structure for the product is established, important conclusions from these results should not be drawn. If the material is shown indeed to be trifluoroboroxine, then the * This work was carried out under Government Contract No. DA-30-069-ORD-2487. I1~ p. BAUMGARTENand W. BRUNS, Ber. 72B, 1753 (1939); 1232 (1941). cz>T. MOELLER,"'Inorganic Chemistry," John Wiley and Sons, Inc., New York 1952, p. 751. ts~ N. V. SIOOWlCK,"The Chemical Elements and Their Compounds, Vol. I" Oxford University Press, London, 1950, p. 396. ~4J H. D. FISHER and I. SHAPIRO, Abstracts of Papers, 138th Meeting American Chemical Society, p. 39N, 1960. t~ H. D. FISHER, W. J. LEHMANNand I. SHAPmO, J. Phys. Chem. 65, 1166 (1961).
153
The accelerated reduction of Np(VI) in chloride media in the presence of platinum that was observed by earlier workers ~s~was confirmed by us. The potential of the couple Pt + 6 C 1 - ~ - P t C l s s- + 2e is - 0 - 7 3 V c8~ which is sufficiently positive for reduction of Np(V1) to the (V) and (IV) states. An analysis by emission spectroscopy of a solution resulting from the addition of a piece of Pt wire to a Np(VI) solution in HCI, showed the presence of platinum in solution. The absorption spectrum of this solution showed that some Np(IV) was present in addition to Np(V) and a large absorption peak occurred in the U.V. at 262-5 m/~; PtCIrt-(aq) is reported to have an absorption maximum at 262 m/~.cs' As a further test on the mechanism of reduction in the presence of platinum, a piece of carefully cleaned platinum wire was weighed on a micro balance and then placed in contact with a 2" 15 × 10 -t M Np(VI) solution in 2 M HCI. After one week the platinum was removed, washed and reweighed; the concentrations of Np(V) and Np(IV) in the solution were determined spectrophotometrically as 1.80 × 10 -3 M Np(V) and 0.30 × 10-aM Np0V). Asimple calculation shows that 2.81 mg of Pt would be required for this reduction. The loss of weight of the Pt wire was measured to be 2-77 rag. This agreement is well within the experimental errors. It would be of interest to repeat these observations using gold metal. It is therefore concluded that the reduction in the presence of Pt is not due to catalysis of the CI- reduction but to reduction by platinum itself. There is no evidence from our work that reduction of Np(VI) by chloride takes place to any significant extent, either in the presence or absence of platinum. DONALD Corms Chemistry Division BRIAN TAYLOR~ Argonne National Laboratory Argonne, Illinois ~ Present address, Chemistry Division, AERE, Harwell, England. ts~ j. j. KIRKLANDand J. H. YoE, Anal. Chim. Acta. 9, 441 (1953).
The reduction of titanium tetrachloride by sodium dispersed on alumina (Received 24 May 1961 ; in revised form 17 July 1961) IT IS known that TiCI4 can be reduced to metallic Ti by the action of sodium, tl~ To obtain a highly active product it has been recommended to use a sodium dispersion prepared by impregnating alumina or sodium chloride with molten sodium, c2~ Indeed, on reacting liquid TiCI, with such a dispersion, a black product was obtained. It is specifically stated that the reaction temperature should be held between 125-200°C. When this precaution was not taken, ignition occurred, the reaction being highly exothermic. On using a lithium dispersion instead of a sodium dispersion violet TiCls was obtained. It is surprising that the relatively small difference in the net electronegativity of Na and Li should cause the reduction of Ti ~v by three additional oxidation states. Indeed, very early, ~3) doubts were raised whether the reduction product obtained under relatively mild conditions was not TiCIt rather than Ti. Since the product from the reaction of TiCI4 with finely dispersed Na shows catalytic properties, it has been thought necessary to check its identity. The analysis of the mixture, which in addition to alumina possibly contains Ti °, TiCI2, Na and NaCI, is not straightforward. It is however possible to distinguish between TiCI, 4- 2Na and Ti ° by first decomposing the TiCI~ and Na with hot NaOH solution. Any metallic Ti present will not react. ~ Both TiCI2 and TiCla will be oxidized to Ti Iv under evolution of hydrogen. ~j The metallic ~1~F. C. ROBINSONand C. C. HUTCHINS,J. Amer. Chem. Soc. 6, 74(1884). M. A. HUNTER,J. Amer. Chem. Soc. 32, 330 (1910). D. LEvy and L. HAMBURGER,Z. Anorg. Chem. 87, 209 (1914). tz~ High Surface Sodium, National Distillers Chemical Co. Ashtabula, Ohio, 1953. is~ O.V.D. PFORDTEN, Ann. Phys. 237, 201 (1887). ~4~ L. WEISSand H. KAISER, Z. Anorg. Chem. 65, 345 (1910). i5l EBELMAN,Ann. chim. phys. 20, 385 (1847).
154
Notes
Ti can then be determined by dissolving it in hot hydrochloric acid, measuring the amount of hydrogen evolved and titrating the Ti m with Fern. ~6) This method is complicated by the fact that some of the nascent hydrogen reduces Ti iv formed in the primary decomposition with NaOH, thereby increasing the amount of Ti m and decreasing the amount of hydrogen evolved.'7) Preparation o f the Reduction Product
Alumina ( " A L C O A " grade F-10) was first crushed to pass 120 mesh and then heated for 3 hr at 500°C in a muffle furnace. It was then transferred to the reaction vessel and kept for a further six hours in vacuo at 450°C. It was then allowed to cool to 150°C and mixed with molten sodium. The mixture was stirred in vacuo for about 15 min and a greyish black dispersion was obtained. The dispersion was allowed to cool and TiCI4 was injected through a rubber gasket using a hypodermic syringe. The dispersion was stirred vigorously both during the addition of the TiCI~ and while the mixture cooled. The colour of the dispersion changed to jet black. The dispersion thus obtained could be filled into separate ampoules for testing and analysing or all of the dispersion could be used. Analysis o f the Reduction Product
The black reduction product was decomposed by the addition of 10 ml of ca. 40 per cent aqueous NaOH solution in vacuo. The solution was heated for about 30 min. Under these conditions both TiCI2 and TiCI3 are oxidized to Ti Iv liberating a corresponding amount of hydrogen. Any residual Na is also decomposed. Only metallic titanium is not attacked. The vessel was then cooled by immersion in liquid air and all the gases were pumped off. The vessel was allowed to warm to room temperature and concentrated hydrochloric acid was added in excess. On heating, the metallic titanium dissolved evolving hydrogen and leaving the titanium in the trivalent state. The vessel was then cooled again in liquid air and the amount of hydrogen evolved was measured. The vacuum was then broken and the Ti II! was rapidly titrated with Fe II1 using NH~CNS as an indicator. If a is the number of moles of hydrogen evolved by the action of HCI and b is the number of 2a+b moles of Ti m titrated, then the quantity of metallic titanium originally present is c -4 gmatoms. The method was checked by analysing a synthetic mixture containing 0.64-gm-atoms Ti ° (crushed sponge Ti metal "B.D.H." laboratory reagent), 0.97 mmoleTiCl2 and 40 gin-atoms Na by the method outlined above. The results were: a = 0.67; b -- 1'15; thence c = 0.62 gm-atoms TiL The results are shown in the Table. It will be seen that the highest percentage of Ti ° found was 8'8%. Obviously most of the TiCI~ was not reduced below TiCI2. TABLE Used
Received
AltOs (ml)
Na (rag-atom)
TiCI4 (mmole)
Na:TiCI~
Ti ° (mg-atom)
Ti°:Ti
15 15 15 15 15 7.5 7.5 7.5
90 90 90 90 90 45 45 45
4.5 9'0 18'0 22'5 36-0 9"0 13.5 27
20 I0 5 4 2'5 5 3-33 l "67
0.11 0.26 0-23 0.33 0-66 0-79 0.69 0.72
2'4 2.9 1.3 1.5 1-8 8"8 5'1 2"7
(6) E. KNECHT and E. HIBBERT,Ber. dtsch. Chem. Ges. 36, 1549 (1903). (~) G. PATSCHEKEand W. SC~ALLER,Z. Anorg. Chem. 235, 257 (1938).
Notes
155
Actually the success of the reduction to Ti ° depends on the temperature reached, which is not uniform. The appearance of a flame shows that at least locally temperatures above 500°C were reached. This is also borne out by the observed sublimation of a little violet TiCI~. Stirring during the injection was not sufficient to result in uniform temperature and the surface of the mass was hotter than the bulk. Therefore a comparison of the results at the same ratio Na:TiC1, shows consistently higher yields of Ti ° when smaller quantities were used. If the reaction is carried out under mild conditions, the temperature being kept below 200°C, no metallic Ti was formed. To verify the effect of temperature a dispersion prepared in the usual way was divided into two parts; the first was analysed without further treatment and the other heated for 3 hr at about 500°C. On heating the yield of Ti ° had risen from 1"5 per cent to 5.1 per cent. It is quite possible that the Ti ° is not formed through the reduction by Na but by decomposition of TiCk. SCWOMS and Stml)STROMcs~ obtained 5 per cent decomposition when TiCIj was heated in vacuo to 475°C. It follows that ordinarily even finely divided Na does not reduce TiCI, below TiClv
Petrochemical Laboratory of the National Council for Research and Development and of the Physical Chemistry Department Hebrew University, Jerusalem
C. EDEN H. FEILCHENFELD D. ZEHAVX
~' W. C. SCHUMBand R. F. SUNDSTROM,J. Amer. Chem. Soc. 55, 596 (1933).
The product of reaction of BF 3 with BzO3* THE FORMATION of trifluoroboroxine, (BOF)s, was first reported by BAUMGARTENand BRims '1,2,s'. The material was reported as a product of reaction of BFs with a number of oxides including BtOs and SiO~. Recently a report suggests that trifluoroboroxine is stable only below - 1 3 0 ° and decomposes rapidly above this temperature to give BFs and B203 '',s~. This leads us to feel that a report of our experiments and observations on the product (hereafter written as product) of the BFs-B=Os reaction is warranted. Boron trifluoride was allowed to react with BzOs and SiO2 in a flow system at 450 ° in the manner outlined in Ref. 1. The white solid product, collected in a cool portion of the system at room temperature, was used in further studies. The product was stable for days at room temperature but melted at about 80 ° with decomposition to B20 8 and BFs. As found by BAUMGARTENand BRLrNS, the material contained B, O and F, but always more BzO t than BFs. A typical analysis showed the ratio of BtOa to BEt to be 2"19. An attempt was made to measure the equilibrium constant between BFs and the tacky mixture of B~Os and product at 80 °. However, the reverse reaction, B2Os(s) + B F , ~ product was very slow at 80 ° and the results were not completely definitive. The heat of formation of the product was determined by measuring its heat of solution in both water and CHnOH after correcting for the heat of solution of the excess B~Os. Assuming that the product was trifluoroboroxine, the entropy of the material was calculated. The following table gives a summary of the properties observed, calculated and estimated for (BOF)s. Until a definite proof of the structure for the product is established, important conclusions from these results should not be drawn. If the material is shown indeed to be trifluoroboroxine, then the * This work was carried out under Government Contract No. DA-30-069-ORD-2487. I1~ p. BAUMGARTENand W. BRUNS, Ber. 72B, 1753 (1939); 1232 (1941). cz>T. MOELLER,"'Inorganic Chemistry," John Wiley and Sons, Inc., New York 1952, p. 751. ts~ N. V. SIOOWlCK,"The Chemical Elements and Their Compounds, Vol. I" Oxford University Press, London, 1950, p. 396. ~4J H. D. FISHER and I. SHAPIRO, Abstracts of Papers, 138th Meeting American Chemical Society, p. 39N, 1960. t~ H. D. FISHER, W. J. LEHMANNand I. SHAPmO, J. Phys. Chem. 65, 1166 (1961).