Pesticide Chemistry in the 20th Century - American Chemical Society

5 The s-Triazine Herbicides

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on February 25, 2018 | https://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0037.ch005

ENRICO KNUESLI C I B A - G E I G Y Ltd., Agrochemicals Division, Basle, Switzerland

The i n v i t a t i o n to give a lecture at t h i s place under these festive circumstances i s a high p r i v i l e g e indeed. The confront ation with t h i s p r i v i l e g e caused concern to the speaker i n so far as a review can hardly furnish much evidence not known to such experts i n the matter as you all, Ladies and Gentlemen, are. What remains without reservation, however, i s the challenge to communicate to you something of the fascination experienced for about twenty years now on the way to and on the way with t r i a z i n e herbicides. With t h i s i n mind, allow me to r e c a l l the scene at the middle of our century. How young an art was chemical weed control then! For a long time man had evidently not f e l t himself so helpless against weeds as against other pests. It i s not by chance that neither thorns nor t h i s t l e s but mosquitoes, gadflies and grasshoppers figure in the range of the ten biblical plagues. Pyrethrum, n i c o t i n e , copper, sulfur were chemical control measures long before chemistry entered the field of weed c o n t r o l . In the late thirties, chemistry - and organic chemistry in parti cular - made a decisive follow-up in the field of insecticides and fungicides, while the field of herbicides was in its infancy. In the mid fifties the range of p r a c t i c a l l y - u s e d organic herbicides was dominated by phenoxyacetic acids; i n t h i s country (USA) the production of 2.4-D had geached an output of 34,000,000 pounds with a sales value of 28x10 $ out of a total herbicide market of 38x10 $ and out of a t o t a l pesticide market of 260x10 $. The range offered to interested herbicide users included, i n 1951, besides 2,4-D the O-alkyldinitrophenols, pentachlorophenol, t r i c h l o r o a c e t i c a c i d , sodium isopropylxanthate, additional chlorophenoxyacetic acids, isopropyl-N-phenylcarbamate, endothal, maleic acid hydrazide and p-chlorophenyldimethylurea. The con cept of a pre-emergence treatment of weeds had just been inaugu rated by the last- mentioned compound. 6

6

6

76

Plimmer et al.; Pesticide Chemistry in the 20th Century ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

5.

KNUESLi

s-Triazine

77

Herbicides

H e r b i c i d e s , 1951 X ι

2,U-D CI-

CCH C00H 2


MCPA

Cl-V \

7-OCH CH OSO Na / 2 2 3

2,U-Di chlorophenoxyethylsulfate, „ Na s a l t

!

CI

-NHCOOiC^H^

Isopropyl

N-phenylcarbamate

3,6-Endoxohydrophthalic a c i d ENDOTHAL

COOH COOH

0 6-Hydroxy~3-(2H)-pyridazinone MH

1 OH

Cl-

-NHCON

/ S

H

3

CH^

3~(h -Chlorophenyl)-l,1-dimethylurea CMU f

T h i s was t h e s t a t u s when we commenced, i n 1 9 5 2 , a p r o j e c t f o r the d i s c o v e r y and t h e development o f h e r b i c i d e s and d e f o l i a n t s . The d e c i s i o n t o i n i t i a t e s u c h a p r o j e c t was t a k e n b y t h e manage ment o f o u r company, t h e n J.R. GEIGY L t d . , a y e a r e a r l i e r . The company h a d a t t h a t t i m e e x p e r i e n c e i n t h e f i e l d o f p h a r m a c e u t i c a l s , d y e s t u f f s, i n s e c t i c i d e s , m o t h - p r o o f i n g a g e n t s , and f u n g i cides. I t i s a p l e a s u r e , a n d an e x p r e s s i o n o f g r a t i t u d e , f o r me t o r e c a l l t h a t D r . Hans G y s i n was t h e i n s p i r i n g a n d e n t h u s i n g l e a d e r o f t h e p r o j e c t and t h a t Dr. A l b e r t Gast c a r e d , w i t h h i g h e x p e r t i s e , f o r a major p a r t o f t h e greenhouse and f i e l d e v a l u a tion. How d i d we a t t a c k t h e p r o b l e m ? I n t h e c o n v e n t i o n a l way: b y e s t a b l i s h i n g work h y p o t h e s e s , b y s y n t h e s i z i n g , by s c r e e n i n g , b y d i s c a r d i n g many compounds.


PESTICIDE C H E M I S T R Y

78

CH C0NHNH 2

2


-NHSCLN

Cl

2

2

/ 3 \ 'CH.

G 25^90

G 2526U

Cl-

Cl-/"S-OSO

-NHCOCON(C H )

N ' CH

3

3

G 25^91

G 2537 * 1

Cl-

-S0 NHC00CH

Cl-

-OCOCON(C H )

/

C H

3

2

N

CH^

G 25^9^

G 25377

Cl- (

CENTURY

H

2

CH C0NHNH

IN T H E 2 0 T H

\ -CH=CHCON(CH ) 3

Cl - /

2

G 25U86

\ -NHCH COOC H 2

2

5

G 25795

I n a f i r s t r o u n d , we t r i e d t o o b t a i n , t h r o u g h s t r u c t u r a l v a r i a t i o n o f known a c t i v e m o l e c u l e s , .new a n d s u p e r i o r b i o l o g i c a l e f f e c t s . We were p a r t i c u l a r l y i n t e r e s t e d t o c h e c k t h e c o n s e quences o f t h e i s o s t e r i c r e p l a c e m e n t o f s t r u c t u r a l e l e m e n t s i n c h l o r o p h e n y l d e r i v a t i v e s as shown above. I n t h e g r e e n h o u s e , d u r i n g b i o l o g i c a l e v a l u a t i o n G 25486 showed d e f o l i a n t p r o p e r t i e s w h i c h l e d t o s t r u c t u r a l v a r i a t i o n work. However, no compound u s e f u l u n d e r p r a c t i c a l c o n d i t i o n s c o u l d be f o u n d . G 25795 d e m o n s t r a t e d r e m a r k a b l e r o o t - p r o m o t i n g a c t i v i t y s o t h a t many f u r t h e r a n a l o g u e s and homologues w e r e synthesized.

O

X

N Ν -NH-i^jI-OC H 2" 5 p

G 25798


5.

KNUESLi

s-Triazine

79

Herbicides

CI


CI-

\-NH-^J-N(C H ) 2

5

2

G 2T902

Cl

G 2580U

Cl

2 5

Ν

2

5

G 258lU

G 2580U r e v e a l e d s u b s t a n t i a l h e r b i c i d a l a c t i v i t y and i n q u i t e e a r l y t e s t s a d i s t i n c t s e l e c t i v e behaviour versus corn and cotton. Why* y°u y a s k , d i d t h e y i n c l u d e , r a t h e r u n e x p e c t e d l y , t h i s s - t r i a z i n e r i n g s y s t e m ? The b a c k g r o u n d h a s a l r e a d y b e e n reported repeatedly. We knew t h a t i n t h e f i e l d o f d y e s t u f f s a n d p h a r m a c e u t i c a l s t h e s u b s t i t u t i o n o f an u r e a b r i d g e b y a b i s - a m i n o - s . - t r i a z i n e g r o u p h a d on o c c a s i o n n o t f u n d a m e n t a l l y changed t h e r e s p e c t i v e properties. m

a

Surfene NH

2 NH

CH -^ 3

Ν

γ

NH Ν

NH

•N'

CH 3

2

Surfene C or Congasine Jensch,Angew.Ch. 50 891

(1937)


PESTICIDE C H E M I S T R Y IN


80

THE

20TH C E N T U R Y

S u r f e n e shows, as an e x a m p l e , s u c h a s t r u c t u r a l c o m b i n a t i o n h a v i n g p r o t o z o i d i c i d a l a c t i v i t y , d e v e l o p e d by a German s c i e n t i s t . So we w e r e i n d u c e d t o t r y t h i s a p p r o a c h , t o o , and we s t a r t e d s y n t h e s i s w o r k i n t h e f i e l d o f £-triazines. The r e s u l t o f o u r p r i m a r y w o r k i n g h y p o t h e s i s was d i s a p p o i n t i n g ; d e r i v a t i v e s b e a r i n g a n i l i n o r a d i c a l s showed no h e r b i c i d a l e f f e c t s . S u r p r i s i n g l y , h o w e v e r , t h e h e r b i c i d a l a c t i v i t y r e a p p e a r e d i n t h e s t r u c t u r e 2c h l o r o - 4 , 6 - b i s - d i e t h y l a m i n o - j ^ - t r i a z i n e , compound G 25804 shown previously. The a w a r e n e s s t h a t we w e r e c o n f r o n t e d w i t h a com p l e t e l y new h e r b i c i d a l m a t r i x w i t h a p p a r e n t l y s u p e r i o r u s e f u l n e s s l e d us t o i n t e n s i v e w o r k a r o u n d t h e s ^ t r i a z i n e r i n g s y s t e m . What a b e a u t i f u l t o o l i s c y a n u r i c c h l o r i d e f o r t h e c h e m i s t working i n chemical synthesis! T h r e e c h l o r i n e atoms o f f e r r e a c t i o n w i t h a l a r g e p r o p o r t i o n of the chemicals l i s t e d i n the B e i l s t e i n Handbook o r t h e C h e m i c a l A b s t r a c t s I n d e x . N o t o n l y t h a t : t h e c h l o r i n e atoms a r e r e a s o n a b l e enough n o t t o r e a c t s i m u l taneously but, under adequate c o n d i t i o n s , s t e p w i s e , a l l o w i n g myriads of p o t e n t i a l combinations. Furthermore: cyanuric c h l o r i d e has b e e n and i s a r e l a t i v e l y cheap k e y m a t e r i a l ; i t can be p r o d u c e d q u i t e e a s i l y f r o m s u c h b a s i c m a t e r i a l s as c h l o r i n e and h y d r o c y a n i c a c i d . As we a s s e m b l e u n d e r t h e a u s p i c e s o f t h e A m e r i c a n C h e m i c a l S o c i e t y , y o u may a s k w h e t h e r i t has n o t b e e n a b o r i n g t a s k t o d e a l w i t h t h i s c h e m i s t r y w h e r e t h e r e a c t i o n scheme i s u s u a l l y quite transparent. No d o u b t , t h e m a j o r a t t r a c t i v e n e s s has b e e n and i s t h e s t r u c t u r e / a c t i v i t y e v a l u a t i o n and t h e r e s p e c t i v e de ductions. B u t now and t h e n i t o c c u r r e d t h a t a r a t h e r n i c e u n e x p e c t e d c h e m i c a l o f f s p r i n g r e s u l t e d f r o m t h i s w o r k , and t h e c h e m i c a l a c c e n t o f o u r m e e t i n g may j u s t i f y t h e q u o t i n g o f some examples: We i d e n t i f i e d t h e s t r u c t u r e o f a s i d e p r o d u c t o b t a i n e d i n a l i q u i d phase p r o c e s s f o r the p r o d u c t i o n of c y a n u r i c c h l o r i d e ; t h i s t e t r a m e r o f c h l o r o c y a n had n o t b e e n d e s c r i b e d b e f o r e and we studied i t s r e a c t i v i t y :

CI Ν

CI-

1

Ν

ν-

Cl Cl

We i d e n t i f i e d a y e l l o w compound w h i c h p o i s o n e d f o r a c e r t a i n time the c a r b o n - c a t a l y s t i n the t r i m e r i z a t i o n of chlorocyan as c y a m e l u r i c c h l o r i d e :


5.

KNUESLi

s-Triazine

Herbicides

81

CI

Cyameluric

chloride


CI

We f o u n d t h a t

cyanuric

chloride

reacts

easily

but

controllable

manner w i t h d i m e t h y l f o r m a m i d e , CO^ b e i n g

The

was

reaction

fully

elucidated

l a t e r by

in

a

evolved.

H.Gold:

CI

c i - k > JJ-ci Ν 3 HCON(CH ) 3

2

0CHN(CH ) C1 3

[

2

Cl(CH ) NCHO-k J-OCHN(CH ) Cl ] 3

N

2

3 HCON(CH

3 C0

+

2

3

3

3*2

|^(CH ) NCH=N-CH=N(CH ) 3

2

H.Gold,

But l e t myriads

us

herbicidal

activity

under p r a c t i c a l Starting ion

return

of possible

to

to

the

3

2

problem of

956

(i960)

selecting,

dérivâtes,

9

and from t h e s e ,

CI

J

Angew.Chem. Jg

2 k,6-s-triazine

out

of

the

t h o s e which have

those which w i l l

be

useful

conditions.

from the

structure

a l o n g f o u r main l i n e s

with regard

2

the

o f G 2580U we i n i t i a t e d

i n order

biological

to

explore

the

variat-

consequences

characteristics:


82

PESTICIDE C H E M I S T R Y

IN T H E 20TH

CENTURY


G 2580U

CI

>V-

Pesticide Chemistry in the 20th Century - American Chemical Society

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