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Highly selective partial hydrogenation of 1,3-butadiene on platinized-platinum electrode in ethylenediamine at open circuit
e&c1,ochbninr Al,f#. “01.
Prinkd
in Orcal
27. NO. 7. pp. 861-862,
so3.w/o 1982. Pcrgamon Press Ltd.
w134686,*2/wo86142
1982.
Srhdn.
Q
HIGHLY SELECTIVE PARTIAL HYDROGENATION OF 1,3BUTADIENE ON PLATINIZED-PLATINUM ELECTRODE IN ETHYLENEDIAMINE AT OPEN CIRCUIT NORIAKI KUBOTA
and
HIDEAKI KITA
Departmentof Chemistry,Faculty of Scienw, Hokkaido (Received
25 August
University,Sapporo 060,Japan
1981; in revised form 7 December
1981)
Abstract-It was found thatplatinized-platinum in ethylmediamine(EDA) is extremely selective (ca 93 %) for the partial hydrogenationof 1.3-butadiene, giving three isomericbutenesin a ratio of I-butene: trans-2butene: cis-tbutene = 13.2: 2.5: 1. Such a hightyselectivepartialhydrogenationwould be due to a specific adsorptionof EDA on pt-Pt giving riseto the replacement of the adsorbed buteneswhichwere formedfrom the partial hydrogenationof 1,3-butadiene.
RESULTS
INTRODUCTION
It is well known that Pt or pt-Pt is very active for the hydrogenation of unsaturated hydrocarbons but with poor selectivity for the partial hydrogenation of alkynes[l] or alkadienes, eg, 1,3-butadiene[2], [3]. This short communication describes ihe effect of EDA which causes the high, almost quantitative, selectivity, in the partial hydrogenation on a pt-Pt electrode at open circuit. EXPERIMENTAL The hydrogenation of 1,3-C4H6 (1,3-C;) was carried out at open circuit in a closed circulation system[3], dead space: 27Oml, which contained a Htype cell. To monitor the open circuit potential during the hydrogenation, zinc-amalgam was used as a reference electrode[4]. The solution was EDA with OS M tetraethylammoniumchloride as an electrolyte. A pt-Pt electrode (apparent surface area, 78 cm’) served as a catalyst. After platinization (-20 mA, 20min) the catalyst was washed with triply distilled water and polarized at + 1.8V (us rhe) 10 min, then OV, lOmin, in lN-H2S04, washed thoroughly with the distilled water, and dried in helium atmosphere. The catalyst in the working solution was prereduced with hydrogen gas for one hour and then the hydrogen gas was replaced with helium. Both gases were purified by commercial purifiers. The reaction gas was a mixture of 1,3-C:, hydrogen and helium with various composition (total pressure = 760 mmHg). 1,3-C; was purified in vacuum. The reaction was commenced by circulating the reaction gas through the t’est electrode compartment of the cell. Products, 1-C*Hs, trons-2-CLH,,cis-2-CdHs and n-CIH,o were analysed by a gas chromatograph. When 1,3-C,D, (Merck Scharp and Dohme Canada, Ltd., Montreal, Canada) was used for an isotopic study, each product was separated gaschromassmatographically and subjected to a spectroscopic-analysis. All the reactions were conducted at room temperature.
AND
DISCUSSION
The selectivity, S, for the formation of butenes is defined as S = P,;I(P,;+PCL)I where PC:, and PC4 are totai butenes and normalbutane pressures,respectively. The results are shown in Fig. 1 as a function of the conversion which is defined a% /(PC, + Pc; + p,,,e~kl x 100. Cl -P,,,i One of the important characteristics of the results is that the selectivity of the partial hydrogenation (S) amounts to 93 % and is constant up to the complete consumption of 1,3-C: as shown in Fig. 1. The distribution of three isomeric butenes also remains unchanged during the reaction. These facts indicate that the hydrogenation of the butene is completely prevented over the pt-Pt when immersed into EDA.
1.0,
I
1
A_-._.
----o--
1
Fig. 1. Butene distribution (Xc_) and selectivity (S) for butenes against conversion (“/,).-Initial reaction gas composition; P&; = 8.2mmHg, Pft = 127.4mmHg. . Selectivity for butenes (S), e 1-C; o trans-2-C;, o c&2-C& 861
862
NORIAKI KUBOTAANDHIDEAKIKI~A
The effects of initial hydrogen pressure (Ph) upon S, the butene distribution and the conversion at 5 min are shown in Fig. 2. The hydrogenation activity (ie, conversion) and the partial hydrogenation activity lie, S) are both slightly affected in a positive way by the increase of Ph.
1,3-C; for butenes or butane should take place which is now not the case. Hence, the reduction in the present work must proceed via catalytic scheme proposed previously for the reduction in aqueous solution[3], which includes the adsorbed hydrogen atoms. The adsorbed deuterium atom, D(a), from D, will take part in the isotopic exchange reaction with the solvent by the following steps, D2 (g) + 2Dla) HzNC2H4NHt
+ D(a) =DHNCIHINHz
DHNC,H,NH,
+ H(a)
+ D(a) +DHNC,H,NHD
+ H(a)
and also with the reacting species as, 1,3-&D,(a)
H(a) H(a) + C4HDs(a) + C.+HD, C,HzD&a) C,H,(a)
01 09
The open circuit potential was about + 400 mV us zinc-amalgam electrode. This potential is more positive than the value at which the hydrogen evolution takes place from EDA[S]. by
I
1.9
2.9O
HzNC2H4NH2
10SIC~“fmmHg)
Fig. 2. Xc,, S and conversion (%) at 5min against log (Pg/mmHg), (P&; = 8.2mmHg). A conversion, other symbolsare the sameas in Fig. 1.
This behaviour is entirely different from that observed in the electroreduction of 1,3-C: in aqueous solution or in catalytic hydrogenation in gas phase on platinum. (ie, usually S tends to zero with increasing Pi?, at platinum eIectrode[3] and the catalyst in gas phase[2]). The isotopic study revealed that the hydrogen distributions in each product obtained from 1,3-C4D, + D2 and 1,3-C,D, + H2 are quite the same. In both cases, the hydrogen atoms added to the reactant reveal a random isotopic distribution with maximum at 2H or 4H for butenes or butane, respectively as shown in Table 1. Such a random distribution cannot be expected from the electrochemical mechanism proposed in theelectroreduction of unsaturated hydrocarbons in EDA[5]. Since, in this mechanism, the electroreduction proceeds via addition of solvated electrons to the unsaturated hydrocarbon followed by proton addition from the solvent[5], a simple addition of 2H or 4H to
Table 1. Distribution ofdeutero-species
C4H,D, C,H,.
ineachproduct
+ e-
+ HlNCzH4NH-
++H,.
Thus, the decomposition of EDA will not take place at the present experimental conditions. EDA will participate in a neutral form in the reaction. In our separate voltammetric study, the electrode surface is predominantly covered with EDA[6]. In short, the present high specific partial hydrogenation is explained by the specific adsorption of EDA on a pt-Pt surface which repels the adsorbed butenes formed from 1,3-C: by the partial hydrogenation. A detailed mechanistic study, including the isotopic exchange reaction, is now under investigation.
REFERENCES 1. H. Kita and H. Nskajima,J. &em. Sw., Faraday
Trans. 1,
(77) 2105 (1981). 2. G. C. Bond,G. Webb,P. 8. Wells andJ. M. Winterbottom, J. them. Sac. 3218 (1965). 3. H. Kita, N. Kuhcta and K. Shimazu, Electrochim. Acca 26, 1185 (1981).
(.I. elec4. K. Izutsu and T. Nakamura, Denk-Kqaku rrochem. Sot. Japan) d8 (2), 78 (1980). 5. H. W. Stemberg, R. E. Markby, I. Wender and D. M. Mohilner, J. ekctrochem.
Sot. 113, 1060 (1966).
6. N. Kubota and H. Kita, to be published.
( %)from
1, 3-C4D, Py,3,-c;and P; = 12 rnmHg,at 30min
Product
h,
h,
bz
bS
ha
h,
h,
h7
hs
hg
hlo
n-C& 1-c; trlans-2-c; cis-2-Cb
0.2 0.4 0 0
0.2 5.0 4.4 3.9
0.2 54.6 55.3 47.4
0.2 21.1 21.8 22.4
35.1 10.6 11.0 14.1
24.8 4.9 4.5 6.5
19.9 2.3
11.0 0.8 0.6 1.5
5.8 0.9 0.4 017
1.8
0.9
hj represent C,H,D,
-j for butenes and C,H,D,,_,
for n-butane.
:::
Prinkd
in Orcal
27. NO. 7. pp. 861-862,
so3.w/o 1982. Pcrgamon Press Ltd.
w134686,*2/wo86142
1982.
Srhdn.
Q
HIGHLY SELECTIVE PARTIAL HYDROGENATION OF 1,3BUTADIENE ON PLATINIZED-PLATINUM ELECTRODE IN ETHYLENEDIAMINE AT OPEN CIRCUIT NORIAKI KUBOTA
and
HIDEAKI KITA
Departmentof Chemistry,Faculty of Scienw, Hokkaido (Received
25 August
University,Sapporo 060,Japan
1981; in revised form 7 December
1981)
Abstract-It was found thatplatinized-platinum in ethylmediamine(EDA) is extremely selective (ca 93 %) for the partial hydrogenationof 1.3-butadiene, giving three isomericbutenesin a ratio of I-butene: trans-2butene: cis-tbutene = 13.2: 2.5: 1. Such a hightyselectivepartialhydrogenationwould be due to a specific adsorptionof EDA on pt-Pt giving riseto the replacement of the adsorbed buteneswhichwere formedfrom the partial hydrogenationof 1,3-butadiene.
RESULTS
INTRODUCTION
It is well known that Pt or pt-Pt is very active for the hydrogenation of unsaturated hydrocarbons but with poor selectivity for the partial hydrogenation of alkynes[l] or alkadienes, eg, 1,3-butadiene[2], [3]. This short communication describes ihe effect of EDA which causes the high, almost quantitative, selectivity, in the partial hydrogenation on a pt-Pt electrode at open circuit. EXPERIMENTAL The hydrogenation of 1,3-C4H6 (1,3-C;) was carried out at open circuit in a closed circulation system[3], dead space: 27Oml, which contained a Htype cell. To monitor the open circuit potential during the hydrogenation, zinc-amalgam was used as a reference electrode[4]. The solution was EDA with OS M tetraethylammoniumchloride as an electrolyte. A pt-Pt electrode (apparent surface area, 78 cm’) served as a catalyst. After platinization (-20 mA, 20min) the catalyst was washed with triply distilled water and polarized at + 1.8V (us rhe) 10 min, then OV, lOmin, in lN-H2S04, washed thoroughly with the distilled water, and dried in helium atmosphere. The catalyst in the working solution was prereduced with hydrogen gas for one hour and then the hydrogen gas was replaced with helium. Both gases were purified by commercial purifiers. The reaction gas was a mixture of 1,3-C:, hydrogen and helium with various composition (total pressure = 760 mmHg). 1,3-C; was purified in vacuum. The reaction was commenced by circulating the reaction gas through the t’est electrode compartment of the cell. Products, 1-C*Hs, trons-2-CLH,,cis-2-CdHs and n-CIH,o were analysed by a gas chromatograph. When 1,3-C,D, (Merck Scharp and Dohme Canada, Ltd., Montreal, Canada) was used for an isotopic study, each product was separated gaschromassmatographically and subjected to a spectroscopic-analysis. All the reactions were conducted at room temperature.
AND
DISCUSSION
The selectivity, S, for the formation of butenes is defined as S = P,;I(P,;+PCL)I where PC:, and PC4 are totai butenes and normalbutane pressures,respectively. The results are shown in Fig. 1 as a function of the conversion which is defined a% /(PC, + Pc; + p,,,e~kl x 100. Cl -P,,,i One of the important characteristics of the results is that the selectivity of the partial hydrogenation (S) amounts to 93 % and is constant up to the complete consumption of 1,3-C: as shown in Fig. 1. The distribution of three isomeric butenes also remains unchanged during the reaction. These facts indicate that the hydrogenation of the butene is completely prevented over the pt-Pt when immersed into EDA.
1.0,
I
1
A_-._.
----o--
1
Fig. 1. Butene distribution (Xc_) and selectivity (S) for butenes against conversion (“/,).-Initial reaction gas composition; P&; = 8.2mmHg, Pft = 127.4mmHg. . Selectivity for butenes (S), e 1-C; o trans-2-C;, o c&2-C& 861
862
NORIAKI KUBOTAANDHIDEAKIKI~A
The effects of initial hydrogen pressure (Ph) upon S, the butene distribution and the conversion at 5 min are shown in Fig. 2. The hydrogenation activity (ie, conversion) and the partial hydrogenation activity lie, S) are both slightly affected in a positive way by the increase of Ph.
1,3-C; for butenes or butane should take place which is now not the case. Hence, the reduction in the present work must proceed via catalytic scheme proposed previously for the reduction in aqueous solution[3], which includes the adsorbed hydrogen atoms. The adsorbed deuterium atom, D(a), from D, will take part in the isotopic exchange reaction with the solvent by the following steps, D2 (g) + 2Dla) HzNC2H4NHt
+ D(a) =DHNCIHINHz
DHNC,H,NH,
+ H(a)
+ D(a) +DHNC,H,NHD
+ H(a)
and also with the reacting species as, 1,3-&D,(a)
H(a) H(a) + C4HDs(a) + C.+HD, C,HzD&a) C,H,(a)
01 09
The open circuit potential was about + 400 mV us zinc-amalgam electrode. This potential is more positive than the value at which the hydrogen evolution takes place from EDA[S]. by
I
1.9
2.9O
HzNC2H4NH2
10SIC~“fmmHg)
Fig. 2. Xc,, S and conversion (%) at 5min against log (Pg/mmHg), (P&; = 8.2mmHg). A conversion, other symbolsare the sameas in Fig. 1.
This behaviour is entirely different from that observed in the electroreduction of 1,3-C: in aqueous solution or in catalytic hydrogenation in gas phase on platinum. (ie, usually S tends to zero with increasing Pi?, at platinum eIectrode[3] and the catalyst in gas phase[2]). The isotopic study revealed that the hydrogen distributions in each product obtained from 1,3-C4D, + D2 and 1,3-C,D, + H2 are quite the same. In both cases, the hydrogen atoms added to the reactant reveal a random isotopic distribution with maximum at 2H or 4H for butenes or butane, respectively as shown in Table 1. Such a random distribution cannot be expected from the electrochemical mechanism proposed in theelectroreduction of unsaturated hydrocarbons in EDA[5]. Since, in this mechanism, the electroreduction proceeds via addition of solvated electrons to the unsaturated hydrocarbon followed by proton addition from the solvent[5], a simple addition of 2H or 4H to
Table 1. Distribution ofdeutero-species
C4H,D, C,H,.
ineachproduct
+ e-
+ HlNCzH4NH-
++H,.
Thus, the decomposition of EDA will not take place at the present experimental conditions. EDA will participate in a neutral form in the reaction. In our separate voltammetric study, the electrode surface is predominantly covered with EDA[6]. In short, the present high specific partial hydrogenation is explained by the specific adsorption of EDA on a pt-Pt surface which repels the adsorbed butenes formed from 1,3-C: by the partial hydrogenation. A detailed mechanistic study, including the isotopic exchange reaction, is now under investigation.
REFERENCES 1. H. Kita and H. Nskajima,J. &em. Sw., Faraday
Trans. 1,
(77) 2105 (1981). 2. G. C. Bond,G. Webb,P. 8. Wells andJ. M. Winterbottom, J. them. Sac. 3218 (1965). 3. H. Kita, N. Kuhcta and K. Shimazu, Electrochim. Acca 26, 1185 (1981).
(.I. elec4. K. Izutsu and T. Nakamura, Denk-Kqaku rrochem. Sot. Japan) d8 (2), 78 (1980). 5. H. W. Stemberg, R. E. Markby, I. Wender and D. M. Mohilner, J. ekctrochem.
Sot. 113, 1060 (1966).
6. N. Kubota and H. Kita, to be published.
( %)from
1, 3-C4D, Py,3,-c;and P; = 12 rnmHg,at 30min
Product
h,
h,
bz
bS
ha
h,
h,
h7
hs
hg
hlo
n-C& 1-c; trlans-2-c; cis-2-Cb
0.2 0.4 0 0
0.2 5.0 4.4 3.9
0.2 54.6 55.3 47.4
0.2 21.1 21.8 22.4
35.1 10.6 11.0 14.1
24.8 4.9 4.5 6.5
19.9 2.3
11.0 0.8 0.6 1.5
5.8 0.9 0.4 017
1.8
0.9
hj represent C,H,D,
-j for butenes and C,H,D,,_,
for n-butane.
:::