Is carbon dioxide photoreducible by monoelectronic transfersunder visible light?

Is carbon dioxide photoreducible by monoelectronic transfersunder visible light?

Tetrahedron Letters,Vo1.26,No.38,pp Printed in Great Britain IS CARBON DIOXIDE 4599-4600,1985 PHOTOREDUCIBLE BY MONOELECTRONIC B. Legros and J.P...

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Tetrahedron Letters,Vo1.26,No.38,pp Printed in Great Britain

IS CARBON

DIOXIDE

4599-4600,1985

PHOTOREDUCIBLE

BY MONOELECTRONIC

B. Legros and J.Ph.

0040-4039/85 $3.00 + .OO 01985 Peraamon Press Ltd.

TRANSFERS

UNDER VISIBLE

LIGHT?

Soumillionx

Departement de Chimie, Laboratoire de Chimie Organique Physique, Louvain, 1, Place L.Pasteur, B 1348 Louvain-la-Neuve, Belgique.

Universite

Catholique

de

ABSTRACT : A reaction presented as a photosensitized reduction of carbon diozide is in fact a photooxicidation of the aromatic sensitizers. A photochemical using a coupled The following

reduction

of CO2 into formic

system of electron

scheme was proposed

for the reaction

'.-$I

(I

P where P = perylene p.dicyanobenzene Although transfer

from DCNA'-

be a very simple

system when

In preliminary

:

.CO2

the aromatic

interesting

media

(DCNA) or

(

sensitizers,

leading

in acetonitrile

the physicochemical

steps in a homogeneous ones mimicking

medium.

cri-

It would

photosynthesis

of Tazuke were

indeed reproduced.

from the reaction

medium,

However,

no formic

it was

acid is formed

of the acid could not be CO*. is photosensitized

the acid doesn't

showed

to the radical

(runs 12 and 13). The coupling

(as for the electron

).

excluded

that the reaction

of triethylamine

cases

to us to examine

with the more elaborate 2-5

the results

the origin

in certain

monoelectronic

compared

is carefully

It was confirmed

present

and Kitamura(')

acetonitrile.

CO;- ---) ---, HCOOH

were possible

involving

organized

(runs 1 and '2). Thus,

ferquenching,

objections

experiments

found that, if oxygen

the presence

mechanims

by Tazuke

in aqueous

(Py) and A = 9,lO dicyanoanthracene

to CO*) it seemed

this process

by the way of highly

without

sensitizers

(DCB).

thermodynamic

teria governing

c

:,

A

(Pe) or pyrene

acid was presented

donor and acceptor

: when the light is cut off or

form (runs 3 and 4). Experiments

that the initiation

of the reaction

anions of the sensitizers

of the sensitizers

are not the source

does not lead to formic

is not necessary

of the acid

made

by an electron

in trans-

acid

(runs 5 to 7). Impurities

: the reaction works in other solvents

(run 9). DCNA is known as a photoinitiator

forming

singlet

oxygen

('0,) or superoxide

anion

(Oi-)

(6-8). Run 10 gives benzaldehyde, which may be the outcome of a reaction of stilbene with 1 19 02( ). However, when O2 is produced in the presence of Rose Bengal and stilbene, no formic

4599

4600

acid is found

(run 15) nor is it formed when Oi- is introduced

(run 14) in the presence A higher

consumption

acid is produced. photooxidation behaviors general

of the sensitizers

We can conclude

and fragmentation

have already

to initiate

the reaction

of Pe. is observed

that formic reactions

been detected

in those experiments

acid is one of the products

of the aromatic

sensitizers

where

of very complex

themselves.

(lo) and this type of degradation

Similar

seems to be rather

(runs 8, 10 and 11).

TABLE

Run N"

Experimental

: PHOTOSENSITIZED

Conditions

FORMIC ACID FORMATIONa

Sensitizers

(conc.)x104M.L-'

[ HCOOH I bx103M.L-.

C

1

CO2, air

CH3CN-H20,

2

II

I co2

3 4

1,

I co2 , air

5 6

II II

,

7

II

8

,I

II

9 10

II II

12

II

II

(2.0

- 2.5)

0.95

(2.1

- 2.3)

0

1: Pe

(2.3)

1.15

DCNA

(2.72)

0.90

,

II

PY

(2.27)

1.03

,

0,

Pe-Ste

(2.0 - 57.3)

3.85



Pe

(2.35)

5.50

II

ste

(5.84)

3.10

II

PhCHO

(119)

7.68

'

Pef

(2.15)

0

II

DCNAf

(2.72)

0 0 0

I

,

CH3CN-H20f,

13

Pe-DCNA

II II

DMSO-H20C,

11

,

14

II

,

II

Peg

(2.10)

15

#I

,

II

sth

(57.3)

a. 20 mL of reaction

mixture,

Pyrex vessel

nm); b. Detected

(x>300

with BF3-cyclohexylmethanol; e. St=stilbene; added;

formic

gas bubbling

16 h, high pressure

triethylamine;

of Rose Bengal

added,

g. Without visible

mercury

methylester

c. 95-5, d. Same result with sensitizers

f. with 0,72 M.L-'

h. 3.42.10-2Mole.L-1

during

by VPC as a cyclohexyl

25 June

1985)

by reaction

but without

light;

light, 0.10 Mole.L-'

of K02

light.

S. TAZUKE, N. KITAMURA, Nature, 275, 301 (1978). M. GRAETZEL, Act. Chem. Res., 14;376 (1981). A. HARRIMAN, J. Photochem., 25, 33 (1984). S. TAZUKE, N. KITAMURA, PureTppl. Chem., 56, 1269 (1984). J.M. LEHN, R. ZIESSEL, Proc. Nat1 Acad. Sex USA, 79, 701 (1982‘ 1. A.P. SCHAAP, K.A. ZAKHIKA, B. KASKAR, L.W.M. FUNG,-J. Am. Chem. sot., 102, J. ERIKSEN, C.S. FOOTE, J. Am. Chem. Sot., 102, 6083 (1980). L.E. MANRING, C.S. FOOTE, Tetrahedon Letters, 25, 2523 (1984). H. SUGIMOTO, D.J. SWAYER, J. Am. Chem. Sot., 105, 4283 (1984). )J.J. LIANG, C.S. FOOTE, Tetrahedon Letters, -23;-3039 (1982).

(-Received in France

lamp (Hanau Q300),

obtained

385 (1980).