In the title reaction, at low pCO (5 at), rapid isomerisation of the substrate occurs and a random distribution of deuterium in the reaction products has been found. At 100 at pCO,  about 2/3 of n-hexanal arises from formylation at position 1 and 1/3 from formylation at position 5

Consiglio, Giambattista

Pino, Piero

von Bézard, Denis A.

CHIMIA International Journal for Chemistry

English

CHIMIA

Chimia 28 (1974) Nr. 9 (September) 609Kurze MitteilungenBis zum 15. des Monats bei der Redaktion eingehende Kurze Mitteilungen werden in der Regel am 15. des folgenden Monats veröffentlicht. Es werden auch Manuskripte aus dem Ausland angenommen, Maximalumfang: 6 Schreibmaschinenseiten (alles inbegriffen).Stability and Hydrolysis Constants of N-Hydroxyethyliminodiacetates of the Rare Earths** Received September 13, 1974.** For more details refer to the Ph.D, thesis of F, Chastchain7.SummaryThe stability constants for the 1:1 and 1: 2 complexes formed between the tetradentate ligand N-hydroxyethyliminodiacetate (HIMDA) and the rare earth ions have been determined at 20°C and at a metal concentration of 0.1 M. The hydrolysis of the 1: 2 com­plexes has been investigated at 20°C in 0.15 M rare earth solutions; the protonation constants of the M(HIMDA)jOH!" complexes have approximately the same values between La and Gd, but decrease strongly from Gd through Lu.A large number of complexes of the tetradentate ligand N-hydroxy-ethyliminodiacetate (HIMDA) were investi-/CH.—COOHHO-CHaCHaN HIMDA acidCH,-COOHgated and their formation constants reported1,2. With the rare earths M3+ stable complexes [M (HIMDA)]+ and [M (HIMDA)2]_ are formed. Their formation constants at 25°C and at ionic strenth 0.1 (KNO3) are known3.The hydrolysis of some 1 :1 and 1 : 2 bivalent metal HIMDA complexes1, of the 1 : 2 uranium (IV) complex4, as well as the formation5 of [La (HIMDA) OH] were studied by Martell and coworkers.In connection with a series of papers dealing with NMR studies of rare earth polyaminocarboxylates6, we have determined by pH titration, at high concentration, the formation constants of their 1 :1 and 1 : 2 HIMDA complexes and the protonation constants of their ternary complexes [M (HIMDA) 2OH]2-.Experimental **Syntheses. HIMDA acid was prepared by hydroxyethylation of the Na- imino-diacetate (Fluka) with ethylene oxide8, and recrystallised twice from hot water.Measurements. Potentiometric titration curves were obtained with a Compensator E 388, fitted with a combined glass-calomel Micro­electrode EA 125 U; the sample solutions were placed in a 5 or 20 ml cell EA 876 equipped with a thermostatic jacket (20.00 ± 0,02 °C), and the titrant added with a Microburette E 457 under CO2 free nitrogen (Metrohm equipment). The pH standardization was done by titration of HN03 with KOH (/t = 1, KNO3; adopting a pKL value of 13.949). KML and KMLa were established by titration of a K[M(HIMDA)2] solution with HNO3 4M (metal concentration at50% titration = 0.1M), and K^La by titration of a similar solution with carbonate free KOH 0.7 M10 (metal concentration at 50% titration = 0.15M). The K[M(HIMDA)2] solutions were prepared by adding KOH to the stoichiometric mixture of rare earth nitrate and KH (HIMDA). Each experiment was run at least twice.Calculations. The simultaneous calculation of several stability constants from the titration curve was carried out according to the VARIAT programme with the approximate constants introduced as initial values. The subprogrammes NEWRAP11 and APPROX12 evaluate the theoretical quantities of base or acid required to obtain the pH values measured in the sample during titration.APPROX is an adaptation of the programme described by Perrin and Sayce13. The metal and ligand concentrations are calculated with the recurrent equations (1) and (2) without accounting for the formation of complexes in the initial approximation.[Ma+1] = [MJ |/CMexp/CMcal[L«+11 = CM /CLexp/CLcal(1)(2)CM, CL: total concentration of the metal (ligand), [Mo], [LJ : approximate value for the free metal (ligand) concen­tration.Table 1. Formation and protonation constants of N-hydroxyethyl­iminodiacetate (L) rare earths complexes at 20°, and high concentra- tion (log K« = 8.79, log Kf = 2.44*)M3+ l°g rml** ± 0.2log «ML2*** logKMLa**** ± 0.03La 7.6 5.63 ± 0.03 10.56Ce 7.9 6.22 ± 0.03 10.50Pr 8.0 6.63 ± 0.03 10.52Nd 8.1 6.94 ± 0.03 10.75Sm 8.4 7.49 ± 0.03 10.62Eu 8.3 7.72 ± 0.03 10.64Gd - — 10.72Tb 8.2 7.95 ± 0.05 10.48Dy 8.2 7.96 ± 0.05 10.18Ho 8.2 7.95 ± 0.05 10.08Er 8.3 7.79 ± 0.05 9.73Tm 8.5 7.79 ± 0.05 9.34Yb 8.5 7.71 ± 0.05 9.12Lu 8.6 7.83 ± 0.05 9.04Y 8.1 7.70 ± 0.05 10.15* K® = [HL]/[H][L]andKH = [H2L]/[H][HL],withlu =1 (KNO3)** Kml = [ML]/[M] [L], with [M]total = 0.1 M*** ^ML2 = [ML2]/[ML][L], with [M]total = 0.1 M****KmL2 = [MLs]/[MLa0H][H], with [M]total = 0.15 M610 Chimia 28 (1974) Nr. 10 (Oktober)Results and discussionThe results which were calculated for the HIMDA pro­tonation constants, the rare earth-HIMDA 1 :1 and 1 : 2 formation constants, and the [M (HIMDA)2OH]2— pro­tonation constants are listed in the Table.The formation constants of [M(HIMDA)]+ determined in concentrated solutions are smaller by 0.45 to 0.84 log K unit for the light rare earths and by approxi­mately 0.9 unit for the heavy rare earths with respect to those3 determined at an ionic strength of 0.1. Though the absolute values of the stability constants are not comparable, the media being too different, the relative change in the stability along the rare earth series is maintained. Thompson and Loraas3 admit that HIMDA is tetradentate in these complexes with the hydroxy­ethyl group coordinated to the metal.The formation constants of [M(HIMDA)2]- are smaller by at most 0.32 log K unit with respect to those esta­blished in dilute solution. They increase steadily with the charge density of the cation from lanthanum to dysprosium (2.33 units) and decrease from dysprosium to ytterbium as the result of steric hindrance.The protonation constants of the ternary complexes [M(HIMDA)2OH]2- may be classified into two groups. In the first group (La to Gd) the constants vary less than 0.2 log K unit, while for the second group (Th to Lu) they decrease by 1.7 unit. Gupta and Powell14 showed a^similar decrease of the protonation constants of [M(HEDTA)OH]~, where HEDTA = hydroxy­ethylethylenediaminetriacetate, in the middle of the rare earth series. In both cases it is not possible todecide whether the reacting proton is exchanging with a coordinated hydroxyethyl group, or a coordinated water molecule.We acknowledge the generous support of the Fonds national suisse de la recherche scientifique through grant 2.0490.73.F. Chastellain and André E. MerbachInstitut de chimie minérale et analytique Université de Lausanne, Place du Château 3, CH-1005 LausanneBibliography1 S. Chaberek Jr., R. C. Courtney and A. E.Martell, J. Amer. Chem. Soc.74 (1952) 5057.2 G. Schwarzenbach, G. Anderegg, W. Schneider and H. Senn, Helv. Chim.Acta 38 (1955) 1147.3 L.C. Thompson and J. A. Loraas, Inorg. Chem. 2 (1963) 594.4 G. H. Carey and A. E. Martell, J.Amer.Chem.Soc.90 (1968) 32.5 R. C.Courtney, R. L. Gustafson, S.Chaberek Jr., and A.E.Mar- tell, J. Amer. Chem. Soc. 80 (1958) 2121.6 Part I: A. Merbach and F.Gnâgi, Chimia 23 (1969) 271 ; Part II: A.Merbach and F.Gnâgi, Helv.Chim.Acta 54 (1971) 691; Part III: F. Chastellain and A. E. Merbach, to be submitted to Helv. Chim. Acta.1 F. Chastellain, Ph. D.Thesis No. 176, Ecole polytechnique fédé­rale de Lausanne, 1974.8 J. P. Quinche, Helv. Chim. Acta 56 (1973) 1073.9 M.S.Harned and W. J. Hamer, J. Amer. Chem. Soc. 55 (1933) 2194; R.Näsänen and P.Meriläinen, Suomen Kemistilethi B 33 (1960) 229.10 J. E. Powell and M. A. Hiller, J.Chem.Educat.34 (1957) 330.Il T.Kaden and A.Zuberbühler, Talanta 18 (1971) 61.12 Y. Gfeller, Ph. D. Thesis No. 175, Ecole polytechnique fédérale de Lausanne, 1974.13 D.D.Perrin and I.G.Sayce, Talanta 14 (1967) 833.14 A. K. Gupta and J. E.Powell, Inorg. Chem. 1 (1962) 955.The Hydroformylation of 2-Pentene-5,5,5-d3** Received September 16, 1974SummaryIn the title reaction, at low pco (5 atL rapid isomerisation of the substrate occurs and a random distribution of deuterium in the reac­tion products has been found. At 100 at PcO’ about 2/s of n-hexanal arises from formylation at position 1 and 1/s from formylation at position 5.In the cobalt catalysed hydroformylation of 2-pentene [mixture of cis (43%) and trans (57%) isomers] under conditions in which no isomerisation of the olefinic substrate can be detected1, 76 % of n-hexanal, 19 % of 2-methylpentanal and 5 % of 2-ethylbutanal are ob­tained (Scheme 1).In principle n-hexanal can be formed by attack of CO either at position 1 or 5 and 2-methylpentanal can be formed by attack of CO either at position 2 or 4, but up to now these alternatives have not been investigated.This aspect of hydroformylation is possibly connected with isomerisation of the olefin-catalyst complex3’2CHO5%CH, -*  ch3-ch2-ch,-ch,-ch,-cho 76%I1CHPCO 93 atIICHPH. 80 at -> ch3-ch2-ch2-ch-ch3 n1 ÇIL ch3[Co(CO)4]2 CHO 19%-*  ch3-ch2-ch-ch2-ch3 inwhich might influence the isomeric composition of the reaction products and has therefore not only theoretical but also practical interest. In order to monitor the for­mation of n-hexanal from 2-pentene, hydroformylation of 2-pentene-5,5,5-ds was investigated at low and high carbon monoxide partial pressure5. The content and distribution of deuterium in the reaction products was investigated by mass and nmr spectroscopy.Chimia 28 (1974) Nr. 10 (Oktober) 611Table 1. Hydroformylation of 2-pentene-5,5,5-d3a at different CO partial pressures [Olefin (2 g); [Co(CO)4]2 (0.3 g); mesitylene (20ml); pH> 100 at; temperature 100°C]Pco(at) ReactionTime (hrs.)Carbonyl Pentane, Aldehydes Distributioncompounds yield, %cyields, %c I II III5.5 2100 4.5400b 676 22 70 25 585 4 75 19 679 2 59 29 12a 58% trans, 42% cisb 0.9 g [Co (CO)j]2 were used c Determined by g.l. c.The reaction was carried out as previously described1 and gave the results reported in Table 1. As it is already known, the percent of linear isomer increases with increasing pco from 5.5 to 100 at1, but remarkably at 400 at pco it is smaller than at 100 at.The deuterium content of the reaction products mixture was determined by mass spectroscopy on the anilide derived from n-hexanal, via n-hexanoic acid, and is compared in Table 2 with that of the starting 2-pen- tene.Table 2. Deuterium content (%)a in the n-hexanoanilidePCO ^o dr dg dg d. d. dg D.N.b5.5 1.5 1.7 10.0 80.0 5.9 0.8 0.2 2.90100 2.1 0.5 4.3 91.8 ~ 0 1.2 0.1 2.91Initialpent-2-ene 2.2 0.3 2.3 95.4 - - - 2.91a Value uncertain to ± 2 %b D.N. = average number of deuterium atoms per moleculeThe results show that at low partial pressure of CO, relatively high intermolecular deuterium/hydrogen transfer takes place, while at high CO partial pressureTable 3. NMR-analysis of methyl n-hexanoate: mean number of hydrogen atoms at each carbon atomaP CO <at) CH — cn2- ch2 CH2—CH2—COOR5.5. 1.91 1.63 1.66 1.40 1.40 -100 1.04 1.91 2.00 1.53 1.53 -Calculated for a product resulting from attack of CO at position 1 of the substrate b 0 2 2 2 2Calculated random distribution 2.18 1.45 1.45 1.45 1.45 -a Values uncertain to ± 5% b Only one isomerisation stepit is much lower. In no case was a decrease of total deuterium content noticed, showing that practically no exchange between deuterium of the substrate and gaseous hydrogen takes place.The methyl esters of the acids obtained from the alde­hydes by an already described procedure4 were sepa­rated by g.l.c. and analysed by nmr [in the presence of Eu(dpm)3] to determine the average deuterium content at each carbon atom of the 2-pentene backbone.In Table 3 the results obtained for the esters derived from deuterated n-hexanals are reported.The spectrum of the products obtained at low partial pressure of CO shows no resolved signals and the deu­terium location approximates a random distribution. On the contrary, for the product obtained at high par­tial pressure of CO, the signals are well resolved. As the intensity of the signal of the methyl group corresponds to 1 proton, the amount of aldehyde formed by formyla­tion at position 1 of the starting olefin is about twice as large as the one arising from formylation at position 5*. The formylation rate at position 5 is higher than that at each of the three positions 2,3 or 4. This confirms that, probably for steric reasons, the catalytic complex largely prefers the two terminal positions of the substra­te. Assuming that the catalyst migration along the substrate backbone occurs by an 1,2-hydrogen shift3, the fact that, within the limits of errors, no deuterium has been found at position 4 of the ester indicates that the catalytic complex migrates along the substrate backbone substantially only once before formylation occurs. This is also confirmed by the rather low deu­terium content found for the methylene group at posi­tion 5. The percent of deuterium at position 2 in the ester is also in line with this interpretation.This work confirms that the identical isomeric composi­tion of the reaction products formed at low pco starting with terminal or internal olefins depends on the fact that, at lowpco, isomerisation of the olefin-catalyst com­plex is much faster than hydroformylation.* Similar results were briefly reported for the l-butene-4,4,4-d3 hydro­formylation by M. Bianchi, U. Matteoli and F. Piacenti at a recent meeting (International Symposium on Metals in Organic Chemistry, Venice, 2 to 5 September, 1974).612 Chimia 28 (1974) Nr. 10 (Oktober)The different isomeric composition of the reaction pro­ducts starting with 1-pentene and 2-pentene1 at high Pco (100 to 400 at) is in keeping with the competition between formylation and olefin-catalyst complex iso­merisation occurring, under high pco, at similar overall rates.As previously stated6 the above mentioned differences inlhydroformylation at low and high pco are probably connected to the existence of an equilibrium, influenced by Pco ’ between different catalytic complexes.We are continuing our investigation in order to clarify the structure of the catalytic complexes prevailing at high and low pco respectively and the factors influen­cing the rate of isomerisation of the catalyst-substrate complex and hence the isomeric composition of the hydroformylation products.Denis A. von Bezard, Giambattista Consiglio and Piero PinoEidgenössische Technische Hochschule Zurich Technisch-Chemisches Laboratorium Universitätstrasse 6, 8006 Zurich SwitzerlandLiterature1 F. Piacenti, P. Pino, R. Lazzaroni, M. Bianchi, J. Chern. Soc. (C) 1966, 488.2 F. Piacenti, S. Pucci, M. Bianchi, R. Lazzaroni, P. Pino, J. Amer. Chern. Soc. 90 (1968) 6847.3 C.P.Casey, C.R.Cyr, J. Amer. Chern. Soc.95 (1973) 2240.4 P. Pino, S. Pucci, F. Piacenti, G. Dell’Amico, J.Chem.Soc. (C) 1971,1640.5 P.Pino, F. Piacenti, P.P.Neggiani, Chern. Ind. (London) 1961,1400.

The Hydroformylation of 2-Pentene-5,5,5-d3

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