Photoisomerization of bentazone

Tetrahedron Letters,Vo1.30,No.45,pp Printed in Great Britain

6159-6160,1989

oo40-4039/89 $3.00 Pergamon Press plc

+ .OO

PHOTOISOMERIZATION OF BENTAZONE Klaus Hustert* and Mohammed fur (?kologische Chemie, SchulstraRe

GSF - Institut

Mansour 10, Cl-8050 Freising-Attaching

ABSTRACT: Photolysis of bentazone 1 in non-polar solvents e.g. n-hexane yields the unexpected photoproduct 2. On irradiation in methanol and in water l-methylbentazone and anthranilit acid isopropylamide as a degradation product are observed.

3-Isopropyl-lH-2,1,3-benzothiadiazin_4(3H)-one herbicide

marketed

as bentazonel.

at 224 nm and a weak bentazone

2,2-dioxide

The UV spectrum

of this compound

band at 328 nm. On irradiation

in non-polar

solvents

like n-hexane,

with

toluene

2-isopropyl-2H-1,2,4-benzothiadiazin-3(4H)-one prepared

acid

isopropylamide

with phosgene

through

bentazone

and has tranquilizing

of 2 is confirmed

IH-nmr spectra

q

151.48

13C-nmr-

and a fragment

of 1 and 2 are similar

from the changed

1 has a chemical 6

by IH-nmr-,

2. This compound

activity3.

except

substitution

ppm in 1 is typical

acid

isopropylamide

zone

is not high because

on alkaline

product;

for small differences

for an aromatic

some polymeric

The yield

6159

in the aromatic

amide, whereas

of such compounds

reof

the shift of

as uracil.

of the photorearrangement

is formed

carbon

Fur-

of o-aminobenzenesulfonic

of o-aminobenzenesulfonic

material

of

1 has a

as Mf-(CO-N-C,H,).

ring. The carbonyl

2 is the formation

hydrolysis5.

of the formation

whereas

can be explained

on the benzene

of the urea type carbonyls

of photoproduct

The mass spectrum

to M+-(SO,-N-C,H,),

m/e 155 which

shift of 162.6 ppm, appropriate

ther proof of the structure

a degradation

lamp

is converted

of o-aminobenzenesulfonic

and hypnotic

and MS-data4.

1 shows a base peak at m/e 119 corresponding

gion resulting

absorption

2

base peak at m/e 91 (C,H,NH) The

strong mercury

l,l-dioxide

condensation

1

The structure

used contact

or dichloromethane

to an isomer2,

and Hurmer

shows

a high-pressure

was previously

by Vernin

1 is a widely

as well.

acid

of benta-

isopropylamide

as

It can be assumed that the rearrangement radical

mechanism

radical

formed

tween

the aromatic

product

as well

bond

intra-

or intermolecularly

by l&-irradiation

of this process

the photorearrangement

1-methylbentazone as dimers

either

is broken

ring and a new carboxamide

The details

and water

conditions

proceeds

a sulphamide

and amino group.

like methanol

Under these dation

can attack

carbonyl

solvents

e.g. after

bond is developed

need clarification.

of bentazone

and anthranilic

acid

by a

the sulphur be-

In polar

cannot be observed.

isopropylamide

as a degra-

are formed6.

ACKNOWLEDGEMENT We are grateful

REFERENCES

to Dr. W. V. Turner

for advice

and reading

of this manuscript.

AND NOTES

1. The Pesticide Council,

Manual,

8

th

ed., ed. by C. R. Worthing,

The British

Crop Protection

1987, 63

2. Bentazone

(50 mg) in 6OD ml n-hexane/toluene

40 minutes.

The product

chloromethane/ethyl

was purified

acetate

(5:l) was irradiated

by column

(1:l); colorless

chromatography

prisms,

yield

thraugh

on silica

pyrex

for

gel with di-

ca. 15 %, RF = 0.79,

mp 175 OC 3. J. Vernin, 4. 'H-nmr

R. Hurmer,

Fr. M. 4279,

(90 MHz, CDCl,)

13C-nmr

(20 MHz, CDCl,)

1967 (Chem. Abstr.,

6 1.6 (6H, d), 4.9 6 151.48,

134.51,

68: P 39659 a)

(lH, m), 7.2 (ZH, m), 7.55 134.21,

123.53,

123.38,

(lH, m), 7.8 (lH, m)

122.50,

116.65,

48.83,

21.30 MS (m/e) 240 (M+); vrnax (KBr) cm-l 1685, 1600 5. Colorless 134.0,

oil, mp 166 'C (as N-acetyl

129.55,

6. G. P. Nilles,

(Received in

123.08,

117.96,

M. J. Zabik,

derivative),

117.71,

J. Agric.

46.18,

l"C-nmr

23.60,

(20 MHz, CDCl,)

MS (m/e) 214 (M+)

Food Chem. 23 (3), 410 (1975)

Germany 11 August 1989)

6 144.93,