钴_钨酸钾氧化亚硫酸氢钠反应动力学与机理_英文_

钴_钨酸钾氧化亚硫酸氢钠反应动力学与机理_英文_ Kinetics and Mechan ism of the Reduction of Ξ12 - Tungstocobaltate( III) by Sodium Sulfate by Spectrophotometry Huo Guo yan Li Bao qin ()Depart ment of Chemist r y , Hebei U niversit y , Bao ding 071002 ( ) The kinetics of t he reductio n of 12 - t unn gstoco balte I I Iby so dium sulfite in a queo us acid solu2 Abstract tio n was st udied by spect rop hoto met ry. It was fo und t he reactio n rate is independent of t he co ncent ratio n of 12 - ( ) t ungstoco baltate I I Iand t he o rder wit h respect to t he co ncent ratio n of so dium sulfite is unit y. The reactio n rate decreases wit h decreasing p H of t he solutio n. The rate co nstant s and activatio n parameters of t he rate - deter min2 ing step were evaluated. A mechanism involvin g a p reequilibrium and agreeing wit h t he experimental data was + + + p ropo sed. The catal ytic activit y of t he alkali - metal io ns follows t he o rder K > Na > Li . ( )So dium sulfate Alkali - metal io ns Key words 12 - Tungstoco baltate I I I ( )( ) The reactio ns bet ween 12 - t un gstoco balte I I I abbre . 12 - TC I I Iand different reductant s have been 〔1 - 8〕( ) t he subject of interest fo r years. The reactio n of reductio n of 12 - TC I I Iby so dium sulfite in a queo us 〔1〕buffer acid solutio n has been st udied b y Mahammad Ali et al. We also st udied t he reactio n in no n - buffer a que2 〔1〕o us acid solutio n in t his paper . We got result s different f ro m t hat of Mahammad Ali et al. The rate equatio n derived f ro m t he mechanism is in a greement wit h t he o bserved experimental result s. 1 Exp eriment al 1 . 1 Rea gents 6 - ( ) The co mplex , potassium salt of 12 - TC I ICo W O],was p repared , characterized and standarized 12 40 5 -〔9〕( ) The co mplex , potassium salt of 12 - TC I I ICo W O]as repo rt., was p rapared by o xidatio n of 12 40 6 - Co W O]wit h PbOand it was characterized and standardized. A . R. grade reagent s were used wit ho ut 12 40 2 f urt her p urificatio n . Solutio ns were p repared in do ubly distilled water . The sulfite solutio n was p repared by dis2 solving an app rop riate amo unt of so dium sulfite in do ubly distilled water and standardized by using an excess of io dine solutio n followed by back tit ratio n wit h standard t hio sulf ate solutio n . So dium nit rate , so dium sulf ate , potassium sulf ate , and lit hium sulf ate were used fo r st udying t he effect of io nic st rengt h and catalytic effect of al2 〔10〕 kali - metal io ns. So dium dit hio nate was p repared by t he know n p rocedure 1 . 2 Determin ing React ion Products The reactio n p ro duct s were deter mined by measuring t he U V - V IS abso rbance of t he solutio ns of po ssible ( ) reactio n p ro duct s i . e so dium dit hio nate , so dium sulf ate , so dium sulfite , and 12 - TCI I. The wave - lengt h of abso rp tio n peak of reactio n p ro duct s were co mpared wit h t ho se of know n co mpo sitio n substances mentio ned Ξ 收稿日期 :1997 - 08 - 31 第一作者 :男 ,1964 年生 ,讲师 ,博士研究生 ( ) above . It co nnfir med t he p ro duct s of reductio n of 12 - TC I I Iby so dium sulfite are so dium sulf ate and potassi2 ( ) um 12 - TC I I. 1 . 3 Test f or f ree ra dical Generatio n of f ree radicals during t he co urse of t he reactio n was co nfir med by t he polymerisatio n of acrylo ni2 t rile in aqueo us solutio n . There are t hree solutio ns : o ne is a mixt ure solutio n of so dium sulfite and potassium 12 ( ) () ( ) ( ) ( ) - TC I I I, 1, t he ot her t wo are so dium sulfite solutio n 2and potassium 12 - TC I I Isolutio n 3, re2 spectively . Acrylo nit rile was added in each of t he t hree solutio ns A heavey p recipitate appeared af ter o ne ho ur in () 1, no p recipitate appeared in t he ot hers. 1 . 4 Kinet ic Mea surements ( ) An U V - 3000 spect rop hoto meter Shimadzu , J apanequipped wit h a t her mo stated cell holder was used to mo nito r t he co urse of reactio n by o bserving t he decrease in abso rbance at t he abso rp tio n maximum of 12 - TC ( ) I I I, 388 nm , under t he co nditio n t hat t he co ncent ratio n of so dium sulfite is always in large excess of 12 - TC ( ) () I I I. The temperat ure was co nt rolled to 303 . 15 ?0 . 1K. p H measurement s were do ne wit h a p HS - 2 mo del p H - meter . All t he experiment s are repeatio n under t he same co nditio ns , w hich deviatio n of each result is generally less t han 6 % , The data used in t his paper are averages of t hree independent experiment value . 2 Re sult and Di scus sio n 2 . 1 Determinat ion of the react ion order de pendence on 12 - TC( III) ) ( ) ( ) ( ( Respective plot s of A - A ,ln A - A ,1/ A - A vs. t w here A - A ,and t have t heir usual t ?t ?t ?t ? ) ( ) significancewere show n in Fig. 1 . The plot of A - A vs. t o nly is linear . Therefo re , p seudo - zero - o r2 t ? ( ) der dependence o n 12 - TC I I Iwas co nfir med. When buffer solutio n was used , t he reactio n rate revealed first 6 -〔1〕 o rder dependence wit h respect to t he co ncent ratio n of Co W O]in goo d agreement wit h literat ure12 40 ) ( Fig. 2. ( )Fig. 1 Determination of t he reaction order dependence of 12 - t ungstocobaltate III 3 + - 5 - 1 - 2 - 1 () Co M = 8 . 05 ×10 mol?L Na HSO = 1 . 21 ×10 mol?L p H = 2 . 08 T = 303 . 2 ?0 . 1K 3 ( ) () ( )Fig. 2 Reaction order dependence of 12 - t ungstocobaltate IIIin buffer solution aand in non - buffer solution b 3 + - 5 - 1 - 2 - 1() Co M = 9 . 78 ×10 mol?L Na HSO = 1 . 21 ×10 mol?L p H = 4 . 78 T = 303 . 2 ?0 . 1K3 2 . 2 Determinat ion of the react ion order de pendence of sulf ite co ncent ratio n wit h different co ncent ra2 ( )Fro m abso rbance/ time curves of reactio ns of definite 12 - TC I I I ( )tio ns of sulfite , we can get t he rates , d C/ d t ,w here C is t he co ncent ratio n of 12 - TC I I I under t he co nditio n - 2 - - - ) ( ) ( C/ d t vs lg HSO and TC I I I. Plot s of lg d of SO > > 12 - k / HSO vs HSO were show n in 3 3 obs 3 3 - - Fig. 3 . It show s t hat t he plot of k/ HSO vs HSO is curved. This result is different f ro m t hat earl y re2 3 3 obs 〔1〕- ) ( po rted. The plot of lg - d C/ d t vs. lg HSO is linear wit h a slo pe of 0 . 94 in t he experimental range , t here23 fo re , t he reactio n is first o rder wit h respect to sulfite . () The rate of t he reactio n can be rep resented by equatio n a: - ()a ]- d C/ d t = kHSO 3 obs + Fig. 4 The effect of H on rate Fig. 3 Determination of t he reaction 3 + - 4 - 1Co M = 1 . 31 ×10 mol?L order dependence of sulfite - 2 -3 + - 5 - 1 Na HSO = 1 . 21 ×10 mol?L 3 M = 8 . 05 ×10 mol?L Co () T = 303 . 2 ?0 . 1K () p H = 2108 T = 303 . 2 ?0 . 1K + 2 . 3 The eff ect of H on rate + The effect of H o n rate was show n in Fi g. 4 , a linear relatio nship wit h a po sitive intercep t suggest s t hat t he reductio n follow s a t wo - pat hs kinetics. One pat h is related to t he co ncent ratio n of hydrogen - io n and has a p reequilibrium . The ot her is independent of t he co ncent ratio n of hydrogen - io n . kof t his pat h can be evaluated o - 5 - 1 f ro m t he intercep t o n t he kaxis in Fig. 4 . kf ro m Fig. 4 is 2 . 07 ×10 s in agreement wit h experimental obs 0 ( )value see tab. 1 2 . 4 The eff ect of electrolytes on rate An at temp t was made to verif y t he effect of elect roiyte o n t he reactio n rates. Fo r t his p ropo se , so dium sul2 f ate and so dium nit rate solutio n of different co ncent ratio n were added to t he solutio ns. It was fo und t hat t he rate increase wit h adding so dium nit rate . It may be at t ributed to t he io nic st rengt h effect in agreement t he earlier 〔1〕wo r k. A decrease in rate wit h increasing so dium sulf ate co ncent ratio n was o bserved , w hich may be explained by t he blocking of sulf ate fo r med in t he redo x reactio n . 2 . 5 D iscussion on the react ion mechan ism Based o n t he experiment p heno mena a reactio n mechanism was p ropo sed as follow s : Ka - 2 - +()1 Pat h I HSO ?SO+ H 3 3 k ,slow 1 2 - 2 -() 2 SO?SO3 3 6 - Co W O ]12 40 2 - (One elect ro n of t he unshare elect ro n pair in SOis stimulated to 4 s o r 4 p o rbit to fo r m t wo f ree elec2 3 )t ro ns f ast2 - + 2 - 6 - 5 - () 3 HO + SO+ 2Co W O?2 H + SO+ 2Co WO2 3 12 40 4 12 40 ()We can co nclude f ro m 1 2 - - + ()( )4 SO ]= KHSO ] / K+ H ] 3 e a 3 t a w here e rep resent s equilibrium and t total 2 - ()5 - d C/ d t = k SO]The rate in rate - deter mining step can be exp ressed as follow s : 3 e 1 () () ()On t he basis of equatio n 4and 5, t he rate exp ressio n is given by equatio n 6 - + ()( )6 - d C/ d t = k KHSO ] / K + H ] 1 a 3 t a Pat h I I ( )Similarly k ,slow 0 + -2 - () HSO ?SO+ H7 3 3 6 - Co W O ]12 40 f ast2 - + 2 - 6 - 5 - () 8 HO + SO+ 2Co W O?2 H + SO+ 2Co WO2 3 12 40 4 12 40 () Reactio n 7is t he rate - deter mining step in pat h ?and it s rate can be exp ressed as follow s : - ( )]9 C/ d t = k HSO - d 3 t 0 + ( )K()= k + kk/ K+ H ] 10 obs0 a 1 a + The value of H is much hi gher t han t hat of K, we have a + ()11 k= k+ Kk / H] obso a 1 This result is in goo d agreement wit h p redicted above . 2 . 6 Eval uat ion of the act ivat ion para meters 5 - - ( ) Keeping t he ot her co nditio ns t he same Co WO, HSO ,and p H , t he temperat ure is changed , k 12 40 3 obs can be got f ro m t he abso rbance curves of redo x reactio n at different temperat ures. At anot her p H value , similar experiment s as above were repeated , kat t his p H were got . kand kat different temperat ures were calculated obs o 1 () wit h kf ro m equatio n 11. The data of kand k showed in tab. 1 . obs o 1 Tab. 1 k, k,and kat diff erent temperatures and p H′s obs o 1 - 5- 5- 1T/ K p H K/ 10 k/ 10 k/ 10 obs0 1 303 . 2 2 . 58 1 . 44 2 . 10 2 . 86 2 . 48 3 . 28 307 . 2 4 . 37 2 . 06 2 . 10 4 . 67 2 . 48 5 . 37 311 . 2 2 . 10 6 . 94 6 . 06 4 . 57 2 . 48 8 . 27 2 . 10 9 . 48 315 . 2 8 . 07 9 . 21 2 . 48 12 . 52 319 . 2 2 . 10 11 . 60 9 . 79 9 . 35 2 . 48 14 . 31 2 . 10 19 . 10 323 . 2 15 . 46 19 . 10 - 1 T were show n in Fig. 5 . Activatio n ener gies of t he rate - deter2 Respective plot s of lg kand lg k against o 1 mining step s at 303 . 2 K have been calculated f ro m t he slo pes in Fig. 5 . Activatio n ent halp y and activatio n ent rop y ??of rate - deter mining step s at 303 . 2 K calculated acco rdin g to equatio ns 11 E= ?H + R T , ?S = R l g A a - lg kT / h - 2 . 303 / 2 . 303 and were listed in table 2 , w here l g A is t he intercep t o n t he lg k axis in Fig. 5 , k B B ? and R have t heir usual si gnificance . Negative ?S in pat h I may be at t ributed to t he increasin g hydratio n of 2 - 2 - ?SOand in2 , Po sitive ?S in pat h I may o riginate f ro m t he joint effect of t he increase in h ydratio n of SO 3 3 crease in co ncent ratio n. Tab. 2 Activation parameters of rate - determining step in the redox reaaction at 303 . 2 K - 1?- 1?- 1 - 1Rate const E/ kJ ?mol ?H / kJ ?mol ?S / J ?mol ?Ka k 65 . 42 62 . 90 6 . 38 0 k 110 . 97 108 . 45 - 28 . 42 1 Fig. 6 Fig. 5 Relation between rate constant s of t he Effect of alkali - metal sulfate on rate 3 + - 5 - 1Co M = 8 . 05 ×10 mol?L rate - determining step and temperat ure - 2 - 13 + - 4 - 1Na HSO = 1 . 21 ×10 mol?L 3 Co M = 1 . 31 ×10 mol?L - 2 - 1 () Na HSO = 1 . 21 ×10 mol?L p H = 2 . 10 T = 303 . 2 ?0 . 1K3 - 7p H = 2 . 10 , 2 . 48 K= 1 . 6 ×10 a 2 . 7 Catalysis of al kal i - metal cat ions An at temp t was made to verif y t he effect of alkali - metal io ns o n t he reactio n rates. Fo r t his p urpo se , keep2 - 5 - () ing t he ot her co nditio ns t he same p H , HSO , Co W O, temer pat uret he co ncent ratio n of t he alkali - 3 12 40 + + + + A o ) (metal catio ns A varied individuall y fo r each of t he catio ns Li ,Na and K . Plot s of k/ kvs. co ncent ra2 obs obs A o ( ) tio n of ASOwere linear Fig. 6, w here k, kis k in case alkali sulfate is added o r not , respectively. The 2 4 obs obs obs decrease in rate wit h increasin g alkali - metal sulfate co ncent ratio n is at t ributed to t he blockin g of sulfate io n fo r med in t he redo x reactio n. Effect of alkali - metal io n o n rate increases wit h t he increase in io nic radius at t he same co ncent ratio n fo r different alkali - metal io ns. If t he blockin g of sulfate io n co uld be eliminated , t he effect of alkali - metal io ns o n rate mi ght increase wit h increasing t heir co ncent ratio n. Suppo se t he alkali - metal io nic catalysis o n rate does not exist in t he redo x reactio n and t he influence of alkali - metal io n o n rate is at t ributed to t he effect of io nic - st rengt h , different alkali - metal io ns of identical co ncent ratio n sho uld have t he same rate . Howere , t he result s denyed t he suppo sitio n. Therefo re , we ma y at t ribute t he alkali - metal io nic effect o n rate to t heir catalytic effect . This kind of catal ysis may follow a catio n bridge o utersp here elect ro n t ransfer mechanism 〔4〕+ + wit h t he generatio n of f ree radicals. The catalytic activit y of alkali - metal io n follows t he o rder K > Na > + + + + + Li . This may be explained by t he fact t hat t he size of t he h ydrated catio ns is Li > Na > K . Thus K and + + 〔1〕 Na wo uld be mo re effective t han Li in bridging t he t wo negatively charged reacting species. The aut ho rs t hank Prof . Wan g Anzho u and Prof . Shan J inhuan fo r t heir helpf ul discus2 Ackno wledgement sio n wit h us o n t he p resent wo r k . Ref erence ( ) ( ) 1 Mahammad Ali , Swapan K Saha , Pradyot Banerjee. Oxidation of sulp hur IVby dodeca - t ungstocobaltate IIIin aqueous acid so2 () lution. J Chem Soc Dalton Trans , 1990 , 1:187 ( )2 Adefikayo Ayoko G , Adegboyega Olat unji M. Kinetics and mechanism of t he oxidation of glutat hione by 12 - t ungstocobaltate III () in aqueous solutions. A Preliminary Report . Inorg Chim Acta , 1983 , 80 1 - 2:L15 Susheela Dholiya , Adit ya Prakash , Raj N Mehrot ra. Kinetics and mechanism of oxidation of arsenous acid b y 12 - t ungstocobaltate 3 ( ) () IIIion. J Chem Soc Dalton Trans , 1992 , 5:819 ( ) Gao MinQiu , Zhou BenMao , Xia PeiJ ie , et al . Kinetic and mechanism of t he persulfate reduction by 12 - t ungstocobaltate IIin 4 () aqueous solution. Photograp hic Science and Photochemist r y , 1989 ,8 1:7 Michael J Blandamer , John Burgess , Philip P Duce , et al . Initial state and t ransition state solvation effect s in t he cobaltit un gstate 5 () oxidation of lodide in binary aqueous solvent mixt ure. Transition Met Chem , 1982 ,7 1:10 βAdefikayo Ayoko G , Adegboyega Olat unji. Oxidation of L - cystein , mercaptoacetic acid and - Mercaptoet hylamine by 12 - 6 ( ) () t ungstocobaltate III. Polyhedron , 1983 ,2 7:577 ( ) Swapan K Saha , Manik C Ghosh , Prodyot Banerjee. Kinetics and mechanism of t he reduction of dedecat un gstocobaltate IIIby ox2 7 () alate. The catalytic role of alikali metal ions t hrough outersp here bridging. J Chem Soc Dalton Trans , 1986 , 6:1301 Lennart Eberson. Elect ron - t ransfer reactions in or ganic chemist ry. 4 . A mechanistic st udy of t he oxidation of p - met hoxytoluene 8 ( ) () by 12 - t ungstocobalt IIIate Ion. J Am Chem Soc , 1983 ,105 10:3192 Kenji Nomiya , Ryoichi Kobayashi , Makoto Miwa. An imp roved p reparation and characterization of tet rahedral ligand. Bull Chem 9 () Soc J p n , 1983 ,56 8:2272 10 Cao Xizhang , Zhang Wanhui , Du Yaoguo , et al . Inorganic Chemist ry. 2 :2 nd edition. High educational p ress , 1982 ( ) 11 Shan J in Huan , Liu Tie Ying. Kinetics and mechanism of substit ution reactions of Bis N , N - Diet hyldit hiocarbamatoalkylxant ha2 ( ) tocobalt IIIwit h dip rop ylamine and Di - n - but y - lamine in met hanol. Acta Chimica Sinica , 1994 , 52 :1140 ( ) 12 Swapan K Saha , Manik C Ghosh , Pradyot Banerjee. Kinetics and mechanism of t he reduction of 12 - t ungstocobaltate IIIby for2 mate. Catalysis by alkali metal Ions t hrough outersp here bridging. Inorgan Chimica Acta , 1987 ,126 :29 ) ( ?钨酸钾氧化亚硫酸氢钠反应动力学与机理钴 霍国燕李保芹 () 河北大学化学系 ,保定 071002 ( ) 摘要 采用分光光度法研究了酸性水溶液中钴?钨酸钾氧化亚硫酸氢钠反应的动力学 。结果表明对( ) 钴 ?钨酸钾为零级反应 , 对亚硫酸氢钠是一级反应 , 且随氢离子浓度增加反应速率减小 , 随温度的升高反 应速率增大 。并由此计算出了反应的活化参数, 并提出了合理的反应机理 。碱金属离子的催化性能依次为 + + + K > Na > Li 。 ( ) 关键词 钴 ?钨酸钾 亚硫酸氢钠 碱金属离子 中图法分类法 O 643 责任编辑 赵藏赏 () 上接第 135 页 ) ( Marczenko Z , J ankowski K. Sensitive flotation - sepct rop hotomet ric determination of gold based on t he Gold ?/ bromide/ rho2 4 () damine 6 G system. Anal Chim Acta , 1985 , 176:185 () 苏皮里品柯 A T , 塔纳那依柯 M M 著. 异配位体络合物和异金属络合物及其在分析化学中的应用. 陈国亮 ,柴华丽 ,祝大 5 昌译. 上海 :复旦大学出版社 ,1988 . 142 左本成 ,陈国儒 ,李景印. 分子光谱分析. 石家庄 :河北教育出版社 ,1993 . 252 6 Floatat ion Spectrophotometr ic Determinat ion of Aurum on Isochromat ic Dye Ion Pa ir with Tetra bromof l uoresce in and Rhoda mine 6 G Liu Bao sheng Chen Caiping ( Research Cent re of Physical and Chemical Anal ysis , )Hebei U niversit y , Bao ding 071002 Abstract The floatatio n spect rop hoto met ric met ho d fo r deter minatio n of aurum wit h isochro matic d ye io n ( ) - pair is described. Rho damine 6 G R6 Gwas p ro duced and entered into t he a queo us p hase w hen p H = 515 buffer solutio n is added to t he R6 GAuBr by isop rop yl et her floatatio n. And t hen R6 G?TB F is floated by tet ra2 4 ( ) bro mofluo rescein TB Fwit h toluene . Dissolve t he floatatio n p ro duct in aceto ne and measure t he abso rbance of t ( ) he solutio n at 530 nm. The sensitivit y is raised because of t wo dyes Au?R6 G?TB F = 1?1?1assistant effect . 5 - 1 - 1 The molar abso rp tivit y of t his met ho d is 2 10 ×10L ?mol ?cm . Beer′s law holds in t he range of 0 , 0136 mg/ L wit h a relative standard deviatio n of 2 19 %. The met ho d was applied satisfact rily to t he deter mina2 tio n of aurum in cup rum. Rho damine 6 G Tet rabro mofluo rescein Flotatio n spect rop hoto met r y Key words Aurum 责任编辑 赵藏赏