氟化钛水解Hydrolysis of titanium tetrafluoride

2208 Yv. A. BUSLAEV, D. S. DYER, AND R. 0. RAGSDALE lnovgiinic Cheinistry TABLE V MASS SPECTRA O F HYDROPHOSPHOKYL 1 ~ I F L U O R l l ) l f AND HYDROTHIOPHOSPHORYL DIFLUORIDE ----sPFgH---- ---OPF2H ~ ~ i n / c intensitya Ion m / e intensityam" Ion 102 52.9 SPFzH* 86 40.8 OPFzH' 101 6 .9 SPFz' 85 10.6 O P F 2 83 1 . 6 SPFH+ 69 19.6 PFz+ 82 3 . 2 SPF+ 67 8 . 6 OPFH" 69 28.0 PFZ+ 66 1 0 . 2 OPF+ 63 4 . 2 SP+ 50 1 . 6 PF+ 50 3 . 2 PFf 31 1 . 2 Pf Kel Kel a Intensities are expressed as per cent total ionization, defined as SI, where n refers to all ions with m / e >30 whose intensity is >2Y, of the base peak. A very weak peak a t m / e 32 (<0 .5%) due to P H + was observed. S o peaks a t n t / e 104 ( i . ~ . , POI23 or SIFt) or m l e 88 (PFs) were observed. products. While we have not yet completely evalu- ated the effects of impurities and other conditions on the course of this complex decomposition, i t is reason- able to suggest that the initial decomposition product, OPF3, formed by some unknown route, reacts with the original hydrophosphoryl difluoride to form difluoro- phosphoric acid OPFI + OPFrH ---+ PF3 + FIPO(O1-I) and the difluorophosphoric acid in turn is consumed by reaction with the original hydrophosphoryl com- pound 2OPFzH + FaPO(0H) --+ PFI + OPFj + OPH(0H)p The sum of these tIvo equations 30PFzH + 2PF3 f OPH(OH)1 gives an equation which is in fair agreement with tlie observed yield of phosphorus trifluoride. This scheme is consistent with the observations summarized in Table I and with the results of the decomposition study but is not proven. The reaction may involve rearrangement to the trivalent isomer, F2POH, as the initial step. Hydrophosphoryl difluoride yielded phosphorous acid and silicon tetrafluoride on hydrolysis; the latter is probably due to the reaction of hydrogen fluoride with glass OPF2H + 2Hz0 ---+ OPH(0H)Z + 2H1' 2HF + l/zSiOz --+ l/iSiF4 f H 2 0 The hydrolysis of SPF2H also gave phosphorous acid and in addition hydrogen sulfide. Monothiophosphor- ous acid, SPH(OH)s, is probably formed initially SPFzH + HzO + SPH(0H)z + 2HF and subsequently hydrolyzed to phosphorous acid and hydrogen sulfide SI'H(0H)i + HzO --+ OI'H(OI1)y + II& probably catalyzed by the hydrofluoric acid in the solution. I n both cases the yield of silicon tetrafluoride was not quantitative. Hydrogen was not obtained in any of the hydrolysis reactions showing that the hydrogen atoms are not hydritic. The P-H bond probably maintains its integrity during hydrolysis as in the case of the hydr~ lys i s?~ of PF2H. Both compounds have abnormal Trouton constants and notably higher boiling points than those of the parent fluorides, suggesting that they are associated, possibly through weak hydrogen bonding similar to that suggested for difluorophosphine.' More con- vincing support for association is provided by the concentration dependence of the hydrogen chemical shift and by shifts in the infrared frequencies with phase." All of these effects are greatest for the phos- phoryl compound m-here greater hydrogen-bonded as- sociation is reasonably expected. We hope to present more detailed evidence in a future publication. Acknowledgment.-We thank Mr. G. Bigam for assistance with the nnir spectra and the Kational Rc- search Council (Ottawa) for financial support. (24) I<. W. Rudolph and I<. W. Palmy, I i zurp . Chcin., 6, 1070 ( I Y O i ) . COSTRIHUTION FROM THE DEPARTMENT O F CHEMISTRY, UNIVERSITY OF UTAH, SALT LAKE CITY, UTAH 84112 Hydrolysis of Titanium Tetrafluoride BY YU. A. BUSLAEV,' UXKIEL S. DYER, AND ROSXLI) 0. KAGSIIA1,IC Received June 29, 1967 The hydrolysis of titanium tetrafluoride in various solutions is described. sented for the polynuclear species [TiF4,Ti( OH)4(Ha0)2]. adduct TiF4,2HC(O)N( CH3)a showed the presence of TiFa.HC(O)S( CHs)z-, TiFs.HzO-, and TiFsZ-. adduct was found as a product in dilute hydrogen fluoride solutions of TiF4 in water. water but hydrolyzes in acidic solutions. In a 4OT0 TiF4 aqueous solution evidence is prc- An F19 study of the supernatant liquid from the hydrolysis of the The cis-TiF4.2HpO The hexafluorotitanate ion is stable in Introduction tions of Ti(IV).* It was also noted that the hexafluoro- titanate ion was not stable in aqueous solutions but was rapidly hydrolyzed to TiOFJ2-- and more slo\vly to ( 2 ) V. Caglioti, L. Ciavatta, and A. Libereti, J . lilorg. ,Vvzicl. Chein., 15, The species TiOF4"-, TiOFf, TiOF2, and TiOF3- \vere reported to be present in hydrogen fluoride solu- (1) Soviet scientist from the PI'. S. Kurnakov Institute, >Ioscow, on a Scientific Exchange Program between the National Academy of Sciences of the U.S.A. and the U.S.S.R. 115 (ltr60). Vol. 6, No. 12, December 1967 HYDROLYSIS O F TITANIUM TETRAFLUORIDE 2209 I \.; L.--_____I I I -188 -169 PPm Figure l.-F1g high-resolution spectrum of a 40% TiF4 aqueous solution a t -40". Chemical shifts with respect to external CFCl,. other less fluorinated species. However, another study3 indicated that the extent of hydrolysis of TiFe2- in aqueous solution is very limited. Equivalent con- ductance and pH measurements suggested that in the following equilibrium n was much less than 1 TiF2- + nHzO e TiFa-,(OH),2- + n H F Buslaev and co-workers4 studied the three-com- ponent system consisting of water, hydrogen fluoride, and titanium dioxide. A compound corresponding to the stoichiometry TiOFz. HzO was isolated from the solid phase. From conductivity studies of aqueous solutions of hydrofluoric acid and TiOz, the following species were reported to be present: H [TiF4(OH) (HzO) 1, H[TiF6.H20], and Hz[TiF6]. Owing to the uncer- tainty concerning the species present in the titanium- (1V)-hydrogen fluoride-water system, we have studied the hydrolysis of titanium tetrafluoride using fluorine- 19 nuclear magnetic resonance spectroscopy. In this paper the fluorine resonance spectra of various tita- nium tetrafluoride solutions are described. Experimental Section Materials.-Titanium tetrafluoride obtained from Allied Chemical Corp. was used without further purification. TiF4.2- H C( 0 )N (CH3)z and TiF4.2 (4- CH3ChH4NO) were prepared by the method of Muettertiesa6 The hexafluorotitanate ion was prepared in aqueous solution by addition of XH4F to TiF4. The excess XHIF was removed by washing with a CH30H-H20 mixture. Analyses.-Analysis of the solutions was determined by a previously described procedure.6 Instrumental Data.-The fluorine nmr spectra were obtained (3) K. H. Schtnitt, IS. I,. GI-ow, and I t . U. Brown, J . A m . Chem. Soc., 82, (4) Yu. A. Buslaev, V. A. Bochkayeva, and X. S. Nikolaev, Izv . A k o d . ( 5 ) E. L. Muetterties, J . A m . Chein. Soc., 8 2 , 1082 (1960). (6) N. S. Nikolaev and Yu. A. Buslaev, Zh. Neorgan. K h i m . , 4 , 205 (1Y59). 52Y2 (1960). A'nzik SSSR, O l d . Khim. N a u k , 388 (lY62). with a Varian A 56/60A high-resolution spectrometer equipped with a V-6057 variable-temperature accessory. The spectra were calibrated in ppm displacements from external CFC13. Results and Discussion The results of an nmr study of a 40y0 TIF4 aqueous solution a t -40' are summarized in Table I. The spec- trum consists of five resonances as shown in Figure 1. The singlet resonance a t - 75 ppm (relative to external CFC13) was assigned to the hexafluorotitanate ion since the chemical shift corresponds to that obtained for an aqueous solution of (NH&TiF6. TABLE I FIg CHEMICAL SHIFTS, COUPLING CONSTANTS, AND RELATIVE INTENSITIES FOR CONCENTRATED AQUEOUS TITANIUM TETRAFLUORIDE SOLUTIONS AT - 40" lie1 Chem shift, Coupling integ ppm constanl. inten- sities, Comparison of (external cps Multiplet % multiplet intensities CFCla ref) (for F-F) Triplet 7 (triplet : triplet) -188" 36" Triplet 7 1 : l -129 36 Doublet 52 (doublet: quintet) - 95 36 Quintet 13 4: 1 -169 36 Singlet 22 -75 . . . a +l ppm. * 5 1 cps. The quintet and doublet resonances (Figure 1) are assigned to the complex anion TiFj*HzO-. The rela- tive intensities of the doublet to quintet (4: I ) and coupling constant are similar to the spectra obtained for the TiFB.ROH- complex ions.? Previously, Bus- laev and Tcherbakov* reported the presence of the TiFa .H20- ion and TiFG2-- as major products in the (7) R. 0. Ragsdale and B. B. Stewart, Inovg. Chem., 2, 1002 (19631. (8) Yu. A. Buslaev and V. A. Tcherbakov, Dokl. A k a d . N a u k S S S R , 170, 845 (1966). Administrator 铅笔 Administrator 下划线 2210 Yu. A. BUSLAEV, D. S. DYER, AND R. 0. RAGSDALE Inorganic Chemistry hydrolysis of TiF4 in water. The assignment of the TiF6.HzO- was based on analogy to the TiFs'ROH- complexes7 since only the doublet was resolved in the fluorine-19 nmr spectrum. The two triplet resonances (Figure 1) are of equal intensity and the coupling constants are similar to those found for octahedral cis-TiF4 .2B a d d ~ c t s . ~ , ~ ~ ~ ~ At first i t was thought that these resonances were due to unhydrolyzed TiF4. 2Hz0. However, TiFj . HzO- and TiF6?- are major products of the hydrolysis reaction, and there must be a species present which has less than four fluorines per titanium (a Ion- form). Since essen- tially no precipitate was observed, the formation of the low-form TiOn is ruled out. The two triplets were assigned to a low form because no other FI9 resonances ivhich could be attributed to such a species were ob- served. Because of the similarity of the two triplets to the F19 spectra of the cis-TiFA.2B complexes, i t is reasonable to suggest that the structure of the low form is similar to that of cis-TiF4.2B. One would not expect much difference in the chemical shifts of species similar to cis-TiF4.2B. Taking into consideration the relative intensities of the fluorine-19 resonances shown in Table I, an equa- tion is obtained with the stoichiometry 7TiFa + 14Hz0 -+ [TiFa.Ti(OH)r(HzO)s] + (1) This equation is not rigorously balanced since nmr spec- troscopy is not sensitive enough to detect 100% of the fluorine in the system. As a result we cannot rule out the presence of species such as TiFS+(aq) particularly if they are involved in fairly rapid exchange processes. Although based upon concentration of the low form and upon the fact that exchange was not too rapid to detect the other fluorotitanate species, i t does not seem that other low forms could be present in high enough concentrations to account for the fluorine ion which is required for the formation of TiFj.H?O- and TiFE2-. The proposed low form, [TiF4 .Ti(OH)l(HzO)z], has an empirical formula which is similar to TiOF2 .HzO, which has been shown to exist in the solid state.4 \Ye suggest that in solution this fluorine complex is a poly- nuclear species with one part of the molecule having the four fluorines in a cis arrangement 5H30+ + 3.5TiFs.H20- f TiFe2- This structure is consistent with the two 1 : 2 : 1 triplets of equal intensity, with a coupling constant which is similar to that of other octahedral TiFI.2B complexes, and with the chemical shifts which are approximately 10 ppm upfield to that reported for the cis-TiF4.2ROH ad- d u c t ~ . ~ This new complex is consistent with the chem- istry of Ti(1V) which usually forms octahedral corn- plexes with a cis c~nfigurat ion. j" ,~, '~ The proposed (0) 1). S. Dyer and R. 0. Ragsdale, i i ro ig . C h e i i i . , 6, 8 (1967) . (10) 1). S. 12yei and I<. 0. Ragsdale, J P h y s . C'/ IC?JI. , 71, 23OY (1Utii). dimeric species is isomeric with a number of other possible species. The nmr data require a symmetrical arrangement of the ligands coordinated to Ti4+ in Ti(OH)4(HzO)z in order to observe two 1 : 2 : 1 triplets for TiF4. There is another hydroxy-bridged sym- metrical structure which can be drawn and there are some unsymmetrical structures which can be ruled out. Before commenting further on the dimeric species we need to consider other experimental results. Since no TiF4.2Hz0 was detected in aqueous TiF.! solutions, the hydrolysis of TiFl in ethanol was investi- gated. Various amounts of water were added to con- centrated TiFd-CZHZOH solutions. The resulting solu- tions were examined by fluorine- 19 nrnr spectroscopy. In a solution which consisted of lSo/l H20, 3SYh T i I i l , and 47% CeHZOH several hydrolysis products were tlc- tected, but they are of low concentration, and only TiFs.HzO- and TiFj CzHjOH- were positively iden- tified. In all of the solutions which contained less water, TiF4. 2CzHjOH complexes were detected. M-hen a 3G% H 2 0 , 28% TiF4, and 36% CzHjOH solution is obtained, the nmr spectra are similar to those recorded for the TiF4-H20 solutions. In this mixture the major fluorotitanate ions are TiFj .HzO-, TiFj . CeHjOH-, [TiF4 +Ti(OH)4(HeO)z], and TiFti2-. No evidence was found for the TiF4.2H20 complex in the ethanol solu- tions. The hydrolysis of the N,N-dimethylformamide ad- duct TiF4.2HC(0)N(CH3)z was studied. Upon addi- tion of TiFl .2HC(O)N(CH& to water, precipitation occurred immediately. The nmr spectra of the super- natant liquid showed the presence of TiFj .HC(O)N- (CH,)z-, TiFj.HzO-, and TiFc2-. A spectrum of this solution is shown in Figure 2. No low form was de- tected in solution and analysis of the residue indicated that the low form(s) was precipitated since a T i : F ratio - 1 : 2-3 was found. Addition of N,N-dimethylformamide to aqueous TiFI solutions gave similar results (i.e. precipitation and formation of TiFj.HC(0)N(CH3)2-, TiFj.H20-, and TiFs2-). As can be seen from eq 1, aqueous TiF4 solutions are acidic, and the presence of a base such as N,K-dimethylformamide would decrease the acidity of the solution. As the acidity of the solution is de- creased, precipitation of the low form(s) occurs. Simi- lar results were obtained for an aqueous solution of TiF4.2(4-CHSCLH4NO). The low form(s) precipitated and the species TiFj .HzO-, TiFj. (4-CH$jH4NO)-, and TiF& were detected in the solution by F19 nmr spectroscopy. The concentration of TiFj . (4-CHa- CZH4NO)- was low) and only the doublet in the nmr spectrum could be resolved. Hydrogen fluoride-titanium tetrafluoride-water solu- tions were studied in an effort to elucidate the hydrolysis scheme. These data are summarized in Table 11. A solution which has a H F : TiF4 ratio of 1 : 1 gives the following equation based upon the relative integrated intensities of the FL9 signals (eq 2). Administrator 高亮 Administrator 高亮 Vol. 6, No. 12, December 1967 HYDROLYSIS OF TITANIUM TETRAFLUORIDE 221 1 1 PPm Figure 2.-F19 high-resolution spectrum of the supernatant liquid of a TiF4. 2HC(0)lj(CH3)2-Hz0 solution a t -30". Chemical shifts with respect t o external CFC13. TABLE I1 F19 CHEMICAL SHIFTS (PPM) AND RELATIVE INTENSITIES FOR SOME HYDROGEN FLUORIDE SOLUTIONS OF TiF4 IS WATER Tip6%- --- TiFa ' HzO low form"--- - ~ _ _ Chem Relative Chem Relative Chem Relative H F : TiF4 Multiplet shift per cent Multiplet shift per cent Multiplet shift per cent 0 . 5 Triplet - 129 10 Doublet - 94 47 Singlet - 72 22 1 Triplet - 126 8 Doublet - 93 51 Singlet - 73 22 Triplet - 193 10 Quintet - 173 11 Triplet - 198 8 Quintet - 182 11 2 Doublet - 95 13 Singlet - 72 84 Quintet a 3 4 Siiiglct - 71 >96 Coiiceiitration was low, tlic quintet was not detected, a ~ ~ d the relative per c w t was bascd 011 the doublet. 5.5TiF4 + 5.5HF + 5 . 5 H ~ 0 --+ ( 2 ) These results suggest that in hydrogen fluoride solu- tions of the appropriate concentrations, it is possible for TiF4.2Hz0 to exist. Fairly rapid exchange was occurring, and the spectra were obtained a t -50' to help slow down the exchange. One suggested ex- change process is the dissociation of TiF4.2HzO TiF4.2H20 + 3.5TiFb.Hz.O- + TiF8- + 5.5H30+ TiF4.2Hz0 + H20 TiF40H.H20- 4- H30f (3) I n an HF:TiF4 ratio of 3 : 1, both TiFs.HzO- (the quin- tet could not be resolved) and TiFfi2- were detected. The hexafluorotitanate ion was the major species, and the TiFj.HzO- doublet was very broad a t ---5O', indicating rapid exchange. In a titanium tetrafluoride : hydrogen fluoride ratio of 1 : 4, only TiFB2- was observed. It is interesting that the TiF4.2Hz0 complex can be detected in hydrogen fluoride-water solutions of TiFr but not in aqueous solutions of TiF4. This is probably due to the availability of fluoride ions from the dis- sociation of HF. That is, fluoride ion for the forma- tion of TiFj.HzO- and TiFfi2- could come from H F rather than TiF4.2Hz0. Addition of H F would also cause a shift in the equilibrium shown in eq 3. Figure 3.-A comparison of the TiF:. HeO- F1g doublets where A represents the spectrum for an initial H F : TiF4 ratio of 1 : 1 and B represents the spectrum for a HF:TiF* ratio of 2: 1 a t -50". I t should be noted that the chemical shifts for TiF4. 2Hz0 and [TiFd .Ti(OH)4(H20),] are quite similar. The evidence for [TiF4.Ti(OH)4(HzO)z] is not based upon the difference in chemical shifts as the shifts change some with concentration, but our conclusion comes from a consideration of the above results and experiments with TiOn. Instead of adding TiFd to water, one adds hydrofluoric acid to TiOz; results simi- lar to eq 1 or 2 are obtained depending upon the re- spective concentrations of TiOz and HF(aq). The ex- Administrator 高亮 Administrator 高亮 Administrator 高亮 Administrator 高亮 Administrator 下划线 Administrator 高亮 2212 G. M. BEGUN AND A. C. RUTENBERG lnorgunic Chemistry cess TiOz was filtered from the solution before making the nmr measurements. In contrast to the report of Caglioti and co-workers2 and in agreement with Schmitt, et aLJ3 we find that the TiF2- ion is very stable in water. Over long periods of time only a sharp singlet is seen in the F1$ nmr spec- trum of the solution a t room temperature. (”&- TiFe in a 10% HCl solution was prepared and examined by nmr spectroscopy. The spectrum showed the presence of TiF5.HzO- and TiFs’-. These species were in a 2 : 3 ratio. The formation of TiF5.H20- is suggested to occur by the mechanism fast TiFs2- + H30C FjTiFH- + H20 slow FsTiFH- + H20 + FjTiHzO- + HF For TiFe2- to hydrolyze in water, an acid solution is required, because the formation of a hydrogen bond and subsequent formation of H F helps to break the Ti-F bond. This result is consistent with the reported acid-cata- lyzed fluorine exchange between SiFsZ- species. These results are also in agreement with the proposed mechanism for the acid-catalyzed hydrolysis of trans- Co(en)2Fz+ where the formation of a hydrogen bond to fluorine weakens the Co-F bond.I3 In Figure 3 the TiFs.HzO- doublet for an initial H F : TiF4 ratio of 1 : 1 is compared to the doublet for an initial HF:TiFd ratio of 2: 1. Exchange is much faster in the more acidic solution. We suggest that the ex- change is due to exchange of both water and fluoride ion. The fluoride ion exchange is facilitated in more acidic solutions by the initial formation of a hydrogen bond, thus lending additional support for the mecha- nism proposed above. Acknowledgment.-Support of this work by the Air Force, Materials Laboratory, Research and Technology Division, Wright-Patterson AFB, Ohio, is gratefully acknowledged. (1959). (12) E. L. Muetterties and W. 11. Phillips, J. A m Chew. Soc., 81, 1081 (13) F. Basolo, W. 1%. Matoush, and It. G. Pearson, ibid., 7 8 , 4883 (1iJ56) CON rRIBLTIOK FROM 1 H E CHEMISlRI’ DIVISION, OAK I