Development of Functional Organophosphorus Compounds

Chapter 20 Development of Functional Organophosphorus Compounds 1

1

2

Danielle A. Bright, Fred Jaffe, and Edward N. Walsh Downloaded by SUNY STONY BROOK on December 17, 2014 | http://pubs.acs.org Publication Date: April 7, 1992 | doi: 10.1021/bk-1992-0486.ch020

1

Akzo Chemicals Inc., 1 Livingstone Avenue, Dobbs Ferry, NY 10522-3401 2Consultant, 33 Concord Drive, New York, NY 10956

Throughout the years many functional organophosphorus compounds have been prepared for incorporation into polymer systems. In order to prevent loss of these phosphorus-containing additives from the polymer, either through migration or vaporization, one approach has been to provide the phosphorus-containing additive with functional groups which allow it to become chemically bound into the polymer system. Also, modifications of the additives were often required to prevent the phosphorus-containing additive from either interfering with the polymer-forming reactions or destabilizing the polymer. This paper describes some of the approaches recently taken at this laboratory to address these requirements. Also reported is a novel use of elemental phosphorus as a reducing agent. In the course of preparing organophosphorus compounds as flame retardant additives for plastics, a number of requirements were established. First, the additive must be permanantly incorporated. The additive should not migrate from the polymer, it should not be so volatile that it escapes the polymer through vaporization, and it should not be readily extracted under normal use conditions. Second, it should be neutral and non-reacting, in the sense that the additive may not be a salt or an acid that can interfere with the components of the polymer-forming reaction system. Thus, all groups on the phosphorus atom must be bound to the phosphorus atom through a C-P, C-O-P or N-P bond. Third, the additive should have a high phosphorus content, above 10%, and preferably 15-20%. 0097-6156/92Α)486-0248$07.50/0 > 2

10

0

0

4 9 -5°^ Η

+ (n+m) c6^fcHCH

4 9 Η

>

3

C H 0£OÔC H 9

4

0 α

4

9

HO (CH gH0) (^HCH )OH 2

2.

m

2

n

ΓΥΓΡ1 6 (C H 0) ?H + CH 0 + HN(CH CH OH) 2

5

2

2

2

2

^

2

(C H 0) PCH N(CH CH OH) 2

5

2

2

2

2

F i g u r e 1. V i r c o i 82 and F y r o l 6. Two commercial r e t a r d a n t s f o r r i g i d urethane foams. ( 1 , 2 )

2

flame

In Phosphorus Chemistry; Walsh, E., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

20. BRIGHT ET AL

Functional Organophosphorus Compounds

251

Downloaded by SUNY STONY BROOK on December 17, 2014 | http://pubs.acs.org Publication Date: April 7, 1992 | doi: 10.1021/bk-1992-0486.ch020

aldehydes and ketones can be made a v a i l a b l e through a number of well e s t a b l i s h e d chemical r o u t e s , such as those shown i n T a b l e 1. What was s u r p r i s i n g t o u s a t t h e tifoe t h i s r e s e a r c h was begun, was that although these r e a c t i v e , phosphorus-containing carbonyl compounds were known, l i t t l e h a d been r e p o r t e d d i r e c t e d t o t h e i r use t o prepare f u n c t i o n a l phosphorus-containing p l a s t i c s a d d i t i v e s .

The first phosphorus-containing aldehyde d e s c r i b e d i n the l i t e r a t u r e t h a t i s a n e u t r a l n o n - r e a c t i v e compound, i n t h e sense mentioned above, i s d e s c r i b e d by N. Dawson and A. Berger

9

(CH 0) POCH CH 3

5

2

2

SOURCE: Referenced


+

(CH ) 1 3

4


20.

BRIGHT ET AL.


253

phosphorus-containing aldehydes and ketones were the adducts of a dialkyl phosphonate, such as diethyl phosphonate, to a phosphorus-containing aldehyde or ketone, such as d i m e t h y l (3-oxo-l-butyl)phosphonate t o produce 2 - [ ( d i e t h y l ) phosphono]-4[(dimethyl) phosphono]-2-butanol, an u n d i s t i 1 l a b l e o i l . T h i s reaction i s shown i n Eq. 1 of F i g 2. T h i s r e a c t i o n was f i r s t described by P. Tavs ( 1 1 ) , who added d i e t h y l phosphonate t o 4-

2

( C H 0 ) ^ H C (CH OH) CH II 2

CaO

5

2

2

12.5)

+ HC0 H

3

2

3

[(C H 0) PCH-C(CH OH) CH ] 0 CH 2

5

2

2

2

2

2

3

III F i g u r e 3. R e a c t i o n s o f p h o s p h o r u s - c o n t a i n i n g formaldehyde. ( 3 )

Eq.

1

(C H 0) §CH 2H + HNR

Eq.

2

(CH 0) ?CHCH EH CH

2

5

3

2

2

2

2

2

>

with

(C H 0) $CH=CHNR 2

+ 2 HN(C H OH) 2

aldehydes

4

2

5

2

+ H 0

^

2

3

(CH 0) ?^H-CH C[N(C H OH) ] H + 3

2

2

2

4

2

2

H 0 2

F i g u r e 4. R e a c t i o n s o f p h o s p h o r u s - c o n t a i n i n g a l d e h y d e s secondary amines. ( 3 , 12, 13, 14)

with


2

20. BRIGHT ET AL proplonaldehyde on a c r o l i e n .

257

Functional Organophosphorus Compounds was p r e p a r e d from the a c t i o n of t r i m e t h y l

phosphite


S i n c e most of these p r o d u c t s were v i s c o u s , n o n - d i s t i 1 l a b l e l i q u i d s , p u r i f i c a t i o n was difficult. However, based on chemical a n a l y s i s , the r e a c t i o n s do p r o c e e d w i t h s u f f i c i e n t e f f i c i e n c y t o p r o v i d e p r o d u c t s of a c c e p t a b l e p u r i t y and i n good y i e l d . The pathways of these r e a c t i o n s were f o l l o w e d by s e v e r a l t e c h n i q u e s , including the use of i n f r a r e d spectroscopy to f o l l o w the disappearance of the c a r b o n y l and P-H bonds and, where p o s s i b l e , the appearance of the new bonds a s s o c i a t e d w i t h the p r o d u c t s . These a d d i t i v e s were t e s t e d as flame r e t a r d a n t s i s r i g i d urethane foams. The r e s u l t s of one s e t of these t e s t s a r e shown i n T a b l e 4, where the flame r e t a r d i n g performance of these a d d i t i v e s i s compared w i t h t h a t of F y r o l 6. In t h i s t e s t , the l i m i t i n g oxygen index t e s t ( L . 0. I . o r Oxygen I n d e x ) , the a d d i t i v e i s i n c o r p o r a t e d i n t o a r i g i d urethane foam f o r m u l a t i o n a t a l e v e l equal to 20% of the polyol requirement. The r a t i o of polyisocyanate to polyol i s a d j u s t e d t o account f o r the hydroxyc o n t e n t of the p h o s p h o r u s - c o n t a i n i n g a d d i t i v e . A s m a l l p i e c e of the r i g i d foam i s i g n i t e d i n a gas stream which c o n t a i n s v a r i o u s m i x t u r e s of oxygen and n i t r o g e n . The r a t i o of oxygen t o n i t r o g e n is varied until the minimum percentage of oxygen t h a t a l l o w s s u s t a i n e d combustion was determined. T h i s minimum percentage of oxygen i s the l i m i t i n g oxygen i n d e x . The h i g h e r the v a l u e , the more flame r e t a r d a n t i s the m a t e r i a l . The d a t a i n T a b l e 4 show t h a t a l l of these a d d i t i v e s improved the flame r e t a r d a n c e of the r i g i d urethane foam, but not always i n a d i r e c t r e l a t i o n t o the phosphorus c o n t e n t . One of the important commercial flame r e t a r d a n t s f o r p l a s t i c s , the p h o s p h o r u s - c o n t a i n i n g o l i g o m e r F y r o l 99, i s p r e p a r e d by the c o n d e n s a t i o n of t r i s - < 2 - c h l o r o e t h y l ) phosphate, as shown i n F i g . 5. In this reaction, the reagent i s heated to e l e v a t e d temperatures and e t h y l e n e d i c h l o r i d e i s eliminated. The e a r l y d i s c o v e r e r s of t h i s r e a c t i o n , V. V. Korshak e t a l (15) used r e a c t i o n temperatures i n the range of 240-280°C. At these h i g h temperatures, the r e a c t i o n was d i f f i c u l t t o c o n t r o l and i t o f t e n l e d t o an a c i d i c , h i g h l y d i s c o l o r e d p r o d u c t . I f not c a r e f u l l y watched, g e l l e d m a t e r i a l s c o u l d form. I t was l a t e r found

>

ÔH

-K\

3

2

2

2

tris

2

+

2

2

2

C1CH CH C1

2

2

2

2

3

Fyrol

n

Δ

2

^ > Na C0

Thermal c o n d e n s a t i o n o f ( 1 5 , 16, 17)

2

Î-0CH CH C1

2

c.

2

^0CH CH C1

2

^0CH CH C1

2

Ο ÔCHoCHpCl

b.

a.

A c i d R e l e a s i n g Groups

(n+1)

Condensation



260

PHOSPHORUS CHEMISTRY

l e a d i n g t o the formaton of pyrophosphate l i n k a g e s i n the main c h a i n of the condensate and t o the r e l e a s e of a c e t a l d h y d e . The f r e e acidity i s r e a d i l y removed by d i r e c t r e a c t i o n w i t h e t h y l e n e o x i d e . However, the a n h y d r i d e l i n k a g e s and c y c l i c r i n g s p r o v e d more troublesome, e s p e c i a l l y when the o l i g o m e r i s incorporated in polymer f o r m u l a t i o n s such as f l e x i b l e u r e t h a n e foam f o r m u l a t i o n s . These f o r m u l a t i o n s can c o n t a i n amine c a t a l y s t s , p o l y o l s and w a t e r . Since the water and the hydroxy groups of the p o l y o l s can r e a c t with these l a b i l e e n t i t i e s t o r e l e a s e the l a t e n t a c i d i t y , t h i s r e l e a s e d a c i d i t y can a d v e r s e l y a f f e c t the p o l y m e r - f o r m i n g r e a c t i o n s by reacting with the amine and metal s a l t c a t a l y s t s added t o promote the polymer f o r m a t i o n . A l s o , t h i s r e l e a s e d a c i d i t y can a t t a c k the polymer s t r u c t u r e , as i s sometimes seen as d i s c o l o r a t i o n and f r i a b i l i t y of the polymer. Thus, i t was n e c e s s a r y t o tame t h i s oligomer by removing t h e s e l a b i l e , a c i d - r e l e a s i n g groups and thereby t o make the o l i g o m e r i c a d d i t i v e c o m p a t i b l e w i t h the polymer system. A s e r i e s of t e c h n i q u e s was d e v e l o p e d t o remove both the f r e e a c i d i t y and the l a t e n t a c i d i t y . These t e c h n i q u e s a r e i l l u s t r a t e d i n F i g . 6 and F i g . 6a. I d e a l l y , the a d d i t i o n of e t h y l e n e o x i d e should n e u t r a l i z e any f r e e a c i d i t y , as shown i n Eq. 1, and the a d d i t i o n of water or a l c o h o l s t o the o l i g o m e r s h o u l d open the five-membered r i n g s and a t t a c k the a n h y d r i d e l i n k a g e s t o r e l e a s e all l a t e n t a c i d i t y ( 1 8 ) . An o l e f i n o x i d e , such as e t h y l e n e o x i d e , should then be a b l e t o remove t h i s r e l e a s e d a c i d i t y . These r e a c t i o n s a r e shown i n Eq. 2 of F i g . 6 and Eq. 3 of F i g . 6a. However, s i n c e most of t h e s e a c i d r e l e a s i n g r e a c t i o n s a r e not instantaneous, the taming of t h i s o l i g o m e r was found t o be somewhat more d i f f i c u l t than d e s c r i b e d . Many of the problems were s o l v e d when, a f t e r t r e a t i n g the o l i g o m e r w i t h water o r e t h a n o l , a L e w i s a c i d c a t a l y s t , such a s t i t a n i u m c h l o r i d e o r s t a n n o u s o c t o a t e , was added d u r i n g the subsequent e t h y l e n e o x i d e a d d i t i o n ( 2 0 ) . T h i s i s illustrated i n Eq. 4 of F i g . 6a. The t r i a l s a s s o c i a t e d w i t h the f i n d i n g of a s o l u t i o n t o t h i s problem a r e d e s c r i b e d i n d e t a i l i n reference 17 and i n the s e r i e s of p a t e n t s shown i n r e f e r e n c e s 18-21. It will be noted that these treatments t o prevent a c i d formation converted the o l i g o m e r from a n o n - r e a c t i v e o l i g o m e r t o one c o n t a i n i n g r e a c t i v e hydroxy groups. One s u g g e s t e d pathway c i t e d i n the above s t u d i e s f o r the removal of pyrophosphate l i n k a g e s from t h i s o l i g o m e r i c condensate was that ethylene oxide could react d i r e c t l y t o i n s e r t i t s e l f i n t o the pyrophosphate bond ( 1 7 ) . T h i s i s i l l u s t r a t e d i n Eq. 2c of F i g . 6. This suggestion was based i n p a r t upon the remediation chemistry and i n p a r t upon i n f r a r e d m o n i t o r i n g of the r e d u c t i o n i n the c o n c e n t r a t i o n of the pyrophosphate bonds r e s u l t i n g from the remediation processing. However, the r e d u c t i o n i n c o n c e n t r a t i o n or the d i s a p p e a r a n c e of the a n h y d r i d e groups i s not unequivocal evidence that ethylene o x i d e i n s e r t s i n t o the a n h y d r i d e bond. In t h i s o l i g o m e r i c system t h e r e are o t h e r pathways f o r the o p e n i n g of the a n h y d r i d e l i n k a g e s . A l s o , t h e r e was no c l e a r i d e n t i f i c a t i o n of


ÔH

261


BRIGHT ET AL.

+ n CÎÎ^CH

—^

2

^(OCH CH ) OH 2

2

n

(OCH CH ) OH


2

b)

^ - O - P Î . + C H OH — > ^ l - O H + ^ O C H 2

5

2

2

n

Jîf^^J(OCH CH ) 2

5

2

+ ÔC H 2

c) ; J - O - P C + C Î § : H

n

OH

5

-^^5OCH CH O5C

2

2

2

F i g u r e 6. P r o c e s s e s f o r removing a c i d and a c i d - f o r m i n g groups from condensed t r i s < 2 - c h l o r o e t h y l ) phosphate. ( 1 7 , 18, 19, 20, 21)

_OÔÇH ά )

N

.

OCH

F v

CH

2

+

h

O^DCH CH OH

o

2

+

X

2

I

+ C H OH 2

5

2

N)CH

2

_g>>CH CH OH

OH

2

2

(OCH CH ) OH 2

-ir

2

2

n

2

2

2

or C H OH 2

3

dS^CH

o

2

>

N

OCH CH

H0 J/>ÇH

2

0 OCH^CHoOH

9

OCH

< ^ Η

2

5

TiCl or

^

neutral

esters

4

Sn(OCC H 7

1 5

)

2

F i g u r e 6a. P r o c e s s e s f o r removing a c i d and a c i d - f o r m i n g groups from condensed t r i s ( 2 - c h l o r o e t h y l ) phosphate. ( 1 7 , 18, 19, 20, 21)


262



the f o r m a t i o n of the p r o d u c t s e x p e c t e d from an i n s e r t i o n of e t h y l e n e o x i d e i n t o the a n h y d r i d e l i n k a g e .

reaction

The i n s e r t i o n of e t h y l e n e o x i d e i n t o a phosphorus a n h y d r i d e bond has been invoked by s e v e r a l a u t h o r s . Examples are shown i n Fig. 7. The f i r s t example of t h i s r e a c t i o n i s shown i n the work of W. H. Woodstock ( 2 2 ) , who e f f e c t e d the r e a c t i o n of e t h y l e n e o x i d e w i t h P«0io t o produce a c l e a r , a c i d i c , water s o l u b l e l i q u i d t h a t p o l y m e r i z e d on s t a n d i n g t o form a s o l i d , r e s e m b l i n g a r t gum. No y i e l d s a r e g i v e n and the s o u r c e o f the a c i d i t y i s not d e s c r i b e d . A l s o , t h e r e i s no c h a r a c t e r i z a t i o n of the bonding formed i n the p r o d u c t of t h i s r e a c t i o n . F i n a l l y , not a l l of the phosphorus (V) o x i d e i s r e a c t e d i n the Woodstock examples. T h i s i n no way impugns the i n s e r t i o n pathway b u t , w i t h the f o r m a t i o n of an a c i d i c p r o d u c t , i t does suggest r e a c t i o n pathways o t h e r than a d i r e c t i n s e r t i o n r e a c t i o n may be more prominent. Another r e f e r e n c e t o the i n s e r t i o n of an a l k y l e n e o x i d e i n t o a p h o s p h o r i c a n h y d r i d e bond i s d e s c r i b e d by A. J . Papa ( 2 3 ) . T h i s r e f e r e n c e s u g g e s t s the i n s e r t i o n of p r o p y l e n e o x i d e i n t o the p h o s p h o r i c a n h y d r i d e bond of a s y m m e t r i c a l dialkyl pyrophosphoric a c i d . Thus, he s u g g e s t s t h a t the major components of V i r c o l 82 may not i n c l u d e s i g n i f i c a n t amounts of the anhydride linkage. As s t a t e d e a r l i e r ( 1 7 ) , i t was s u g g e s t e d t h a t e t h y l e n e o x i d e i n s e r t s i n t o the a n h y d r i d e l i n k a g e s formed i n a s i d e reaction during the condensation of tris (2-chloroethyl) phosphate. However, i n none of t h e s e two l a t t e r c a s e s i s i n s e r t i o n the o n l y pathway a v a i l a b l e f o r removal of the a n h y d r i d e l i n k a g e and, perhaps because of the d i f f i c u l t y i n a n a l y s i i n g such r e a c t i o n mixtures, i n n e i t h e r case i s a p r o d u c t of such a r e a c t i o n unequivocally i d e n t i f i e d . What we c o n s i d e r as the f i r s t u n e q u i v o c a l e v i d e n c e f o r such an i n s e r t i o n r e a c t i o n has now been demonstrated by D. A. B r i g h t and A. M. Aaronson (24). Under c a r e f u l l y c o n t r o l l e d c o n d i t i o n s , they added e t h y l e n e o x i d e t o t e t r a p h e n y l pyrophosphate t o form and t o identify as the s o l e r e a c t i o n p r o d u c t e t h y l e n e g l y c o l bis ( d i p h e n y l p h o s p h a t e ) . T h i s i s i l l u s t r a t e d i n F i g . 8. The r e a c t i o n proceeds a t 70 °C when e t h y l e n e o x i d e i s added t o molten t e t r a p h e n y l pyrophosphate d u r i n g a 10 hour p e r i o d . P y r i d i n e was found t o be an e f f e c t i v e as a c a t a l y s t . The y i e l d i s 87.4%; m.p., 38-40 °C; p u r i t y , 97.2 by HPLC. A s i m i l a r r e a c t i o n of t e t r a p h e n y l pyrophosphate w i t h p r o p y l e n e o x i d e l e a d s t o an 80% y i e l d of the c o r r e s p o n d i n g i n s e r t i o n p r o d u c t , as an o i l y l i q u i d . The r e a c t i o n time was s i x h o u r s a t 70 ° C ; p u r i t y , 96.7% by HPLC. Magnesium c h l o r i d e and stannous o c t o a t e were a l s o shown t o be e f f e c t i v e c a t a l y s t s f o r t h i s i n s e r t i o n reaction. The next a r e a which we i n v e s t i g a t e d i n v o l v e s a r e a c t i o n t h a t i s r e a l l y a v a r i a t i o n of the c o n d e n s a t i o n r e a c t i o n of tris ( 2 - c h l o r o e t h y l ) phosphate. I f the c h l o r i n e - c o n t a i n i n g group i s on one m o l e c u l e , and the second m o l e c u l e i s a c h l o r i n e - f r e e phosphorus e s t e r , the c o n d e n s a t i o n r e a c t i o n can be conducted t o r e l e a s e and alkyl c h l o r i d e and t o form a new p h o s p h o r u s - c o n t a i n i n g e s t e r . T h i s


20. BRIGHT ET AL

1.

P O 4

+ 10

1 0

dH^CH

>

2


CHC1

Polymeric Product Colorless, Slightly Acidic P o l y m e r i z e s on S t a n d i n g . % P 0 = 40

3

2

Q OH R(O^w Ο J^-O-P^ 10^ uR HO

2.

\.

263


CH ^H^H 3

^-0-^+ d£cH

5

CH

O

CH

Q

ÇHo

Η ( 0 Ϊ Η £ Η ) Ο?(OCH ÎH? o5o (CH OHO) H OR OR

3»

Χ

2

2

2

m

R

>î(OCH CH ) oi^

2

2

2

n

F i g u r e 7. I n s e r t i o n o f a l k y l e n e o x i d e s i n t o a p y r o p h o s p h a t e bond. ( 2 2 , 2 3 , 17)

( C H 0 ) f > 0 & ( O C,Hc)o H ) 6

5

2

6

5

(C H 0) §0?(0C H ) 6

5

2

Catalysts

6

5

jq Catalyst R -tH - ^^1( C H 0 ) P O C H C H O P ( O C H ) + C CÎÎ>-CH 70 C

2

2

02

+ CH d8tH

2

3

6

2

^^^^C

5

6

H

2

5

2

2

6

5

0 ) ?O^HCH o5(C H ) 2

2

6

5

: Pyridine MgCl

2

0 Sn(OCC H 7

1 5

)

2

F i g u r e 8. I n s e r t i o n o f a l k y l e n e o x i d e s i n t o a p y r o p h o s p h a t e bond. ( 2 4 )


2

2


264


i s demonstrated i n F i g . 9, Eq. 1, where d i m e t h y l methylphosphonate can react with e t h y l c h l o r o a c e t a t e t o y i e l d mono- o r d i carbethoxymethyl methylphosphonates. I n a s i m i l a r manner, a s i s shown i n Eq. 2, t r i m e t h y l phosphate can r e a c t w i t h e t h y l c h l o r o a c e t a t e t o l i b e r a t e methyl c h l o r i d e and t o form mono-, d i - , and t r i - c a r b e t h o x y m e t h y l phosphates. By c a r e f u l c o n t r o l of t h e ratio of reagents, one can d i r e c t these reaction to yield predominantly a mono-, d i - o r ( i n t h e c a s e o f p h o s p h a t e s ) a t r i carbalkoxymethyl- d e r i v a t i v e . The f i r s t r e p o r t e d a p p l i c a t i o n of t h i s r e a c t i o n i s d e s c r i b e d by A. N. Pudovik e t a l . ( 25) who r e a c t e d t h e e t h y l e s t e r s o f b r o m o a c e t i c a c i d and c h l o r o a c e t i c a c i d w i t h v a r i o u s phosphonate esters. H i s group used molar r a t i o s of t h e phosphonate and t h e haloacetate, and obtained a mixture of t h e mono- and d i carbethoxy alkylphosphonates. In o u r l a b o r a t o r y , a n u c l e o p h i l i c c a t a l y s t was used t o conduct the c o n d e n s a t i o n reaction. A typical reaction e n t a i l e d heating f i v e moles o f d i m e t h y l methylphosphonate w i t h 11.2 moles o f e t h y l c h l o r o a c e t a t e a t 175 °C i n t h e p r e s e n c e o f a c a t a l y t i c amount of tetramethy 1 ammonium chloride catalyst. The r e a c t i o n was f o l l o w e d by t h e amount o f methyl chloride collected in a cold trap. A f t e r about e i g h t h o u r s , 9.7 moles of methyl c h l o r i d e i s collected. A f t e r w o r k i n g up t h e p r o d u c t , 4.15 moles o f bis (carbethoxymethyl) methylphosphonate was i s o l a t e d by d i s t i l l a t i o n . B.p., 148 °C a t 0.3 t o r r . ; t h e 'H-nmr spectrum was i n a c c o r d w i t h t h e g i v e n s t r u c t u r e ; t h e Ρ nmr spectrum was -35 ppm r e l a t i v e t o ortho-phosphoric a c i d ; %P, 11.7, t h e o r y , 11.5. (26) 3 1

A s i m i l a r p r e p a r a t i o n was made u s i n g methyl c h l o r o a c e t a t e . Y i e l d , 312 g ( 6 7 % ) ; b.p., 136-140 a t 0.6 t o r r ; H-nmr spectrum was i n a c c o r d w i t h t h e a s s i g n e d s t r u c t u r e . x

The preparation of methyl (carbomethoxymethyl) methyl phosphonate was conducted w i t h methyl c h l o r o a c e t a t e and an e x c e s s of d i m e t h y l methylphosphonate, u s i n g sodium c a r b o n a t e a s a c a t a l y s t (27) . The r e a c t i o n of t h r e e moles of e t h y l c h l o r o a c e t a t e w i t h one mole of t r i m e t h y l phosphate l e d t o t h e f o r m a t i o n of tris ( c a r b e t h o x y m e t h y l ) phosphate. B.p., 195°C a t 0.2 t o r r ( 2 7 ) . There was no e v i d e n c e condensed w i t h t h e m s e l v e s .

that

the e s t e r s of c h l o r o a c e t i c a c i d

An a l t e r n a t e p r o c e s s f o r p r o d u c i n g such e s t e r s was r e p o r t e d by K. D. C o l l i n s ( 2 8 ) , whereby d i p h e n y l (carbomethoxymethyl) phosphate was p r e p a r e d from t h e r e a c t i o n o f d i p h e n y l p h o s p h o r o c h l o r i d a t e w i t h methyl g l y c o l a t e i n t h e presence of a t e r t i a r y amine, such a s p y r i d i n e o r l u t i d i n e . T h i s i s shown i n Eq. 3.


20.

BRIGHT ET AL.


265

The bis (carboalkoxymethyl) methylphosphonates are d i f u n c tional e s t e r s , which can be c o n v e r t e d t o l i n e a r p o l y e s t e r s when h e a t e d w i t h a d i o l , such as e t h y l e n e g l y c o l , at 180 C i n the presence of a c a t a l y s t , such as stannous o c t o a t e ( 2 7 ) . T h i s i s shown i n F i g . 10, Eq. 1. There i s no e v i d e n c e f o r the a l c o h o l y s i s of the phosphorus e s t e r bonds. An a l t e r n a t e p r e p a r a t i o n , the r e a c t i o n of d i m e t h y l methylphosphonate w i t h bis chloroacetate e s t e r of e t h y l e n e glycol i n the presence of t e t r a m e t h y l ammonium chloride led to a similar linear polyester. This i s also i l l u s t r a t e d i n Eq. 2.


e

The above c i t e d d i o l , when i n c o r p o r a t e d i n t o a flexible polyurethane foam f o r m u l a t i o n at a 5.6% l e v e l (10 phr based on the p o l y o l ) produced a s e l f - e x t i n g u i s h i n g u r e t h a n e foam, based on the Motor V e h i c l e s S a f e t y S t a n d a r d 302 F l a m m a b i 1 i t y T e s t . In addition to u s i n g these p h o s p h o r u s - c o n t a i n i n g ester compounds i n s y n t h e t i c polymer f o r m u l a t i o n s , these e s t e r s , when converted to their corresponding amides, are e f f e c t i v e in aminoplast resin formulations, p a r t i c u l a r l y those suitable for imbedding the a d d i t i v e on c o t t o n . The conversion of these ( c a r b e t h o x y m e t h y l ) methylphosphonates t o the c o r r e s p o n d i n g amides i s shown i n F i g . 11, Eq. 1. In t h i s example, methy1 (carbcmethoxymethy1) methy1phosphonate was d i s s o l v e d i n a c o l d , 4.43 molar s o l u t i o n of anhydrous ammonia i n methanol. A f t e r b e i n g a l l o w e d t o warm t o room t e m p e r a t u r e , the r e a c t i o n mixture was h e a t e d t o 46°C f o r two h o u r s , and the solvent removed by distillation. The residue, methyl (carbamoylmethy1) methylphosphonate, was i s o l a t e d as a s o l i d . This s o l i d product was r e c r y s t a l 1 i z e d from e t h a n o l ; m.p., 50-5°C (27). T h i s compound was a l s o p r e p a r e d by V. E. S h i s h k i n e t a l (29) by heating methyl (2-ethoxy-2-iminoethyl) methylphosphonate h y d r o c h l o r i d e at 50-60°C. T h i s i s shown i n Eq. 2. B i s (carbamoylmethy1) methylphosphonate was prepared in a similar f a s h i o n from 0 bis (carbomethoxymethy1) methylphosphonate and m e t h a n o l i c s o l u t i o n of ammonia. The p r e p a r a t i o n of d i m e t h y l (carbamoylmethy1) phosphate and bis (carbamoylmethyl) methyl phosphate from ammonia and the corresponding ester precursor a r e i l l u s t r a t e d i n Eq. 3a and 3b of Fig. 11. D e t a i l s of t h e i r p r e p a r a t i o n a r e d e s c r i b e d i n r e f e r e n c e 30. Of the s e v e r a l r e a c t i v e flame r e t a r d a n t s f o r c o t t o n , 0,0-dimethyl (N-hydroxymethyl) carbamoyl e t h y l p h o s p h o n a t e , sold commercially as P y r o v a t e x CP, has proven t o be one of the more effective (31-33). When imbedded on c o t t o n i n c o n j u n c t i o n w i t h o t h e r ami n o p l a s t s , i t forms a permanent bond t o the c o t t o n , a bond t h a t can w i t h s t a n d at l e a s t 50 l a u n d e r i n g s . At the a p p r o p r i a t e loading, i t w i l l render the f a b r i c flame r e t a r d a n t , i n a c c o r d w i t h the Federal Flammabi1ity Standard of J u l y 27, 1971. The


266

1.


CH ?(OCH ) 3

3

2

+ ClCH 2oC H 2

2

^ Catalyst

5

+ 2 ClCH 2oC H 2

2

C H § ( O C H ) (OCH 2oC H )+CH C1 3

3

2

2

5

3

CH §(OCH 2oC H ) +2CH Cl

5

3

2

2

5

2

3


Catalyst

2.

(CH 0) P=0 + C 1 C H § 0 C H 3

3

2

2

^ ( C H 0 ) ÔCH ?OC H +CH Cl Catalyst

5

3

+ 2 C1CH $0C H 2

2

2

2

2

5

3

CH 0§(0CH ?0C H ) +2CH C1

5

3

2

2

5

2

3

Catalyst

+ 3 C1CH §0C H 2

3.

(C H 0) 5ci 6

5

2

2

+ H0CH §0CH 2

5

^ Catalyst

0=P(OCH §OC H ) +3CH Cl 2

5

3

3

+ CgHgN —=>•

3

(C H 0) ?OCH §OCH 6

2

5

2

2

3

+

+

[C H NH ][Cl"] 5

5

F i g u r e 9. C o n d e n s a t i o n o f e t h y l c h l o r o a c e t a t e and p h o s p h o r u s e s t e r s . P r e p a r a t i o n of phosphorus e s t e r s of e t h y l g l y c o l a t e . ( 2 5 , 26, 2 7 , 28)

η CH $(OCH §OC H ) +n 3

2

2

5

2

HOCH CH OH 2

^

2

[-0-2cH o|oCH §-OCH CH -] 2

2

2

2

n

Δ + 2n C H O H 2

η C 1 C H,eoCH,CH,0@< C0CH CH 0CCH C1 2

2

2

2

+n C H P ( O C H ) 3

3

5

2

Δ -[0§CH o|oCH ?OCH CH ]CH 2

2

2

2

n

+ 2n C H C 1

3

F i g u r e 10. P o l y c a r b o x y a l k y 1 p h o s p h o n a t e s . Permanent r e t a r d a n t f o r f l e x i b l e u r e t h a n e foams. (26)

flame


3

20. BRIGHT ET AL.



p r e p a r a t i o n o f t h i s compound representative co-condensation a m i n o p l a s t s i s shown i n Eq. 2.

i s shown reaction

267

i n F i g . 12, Eq. 1. A of t h i s compound w i t h

In a screening test, where methyl (carbamoylmethy1) methylphosphonate was i n c o r p o r a t e d i n t o an aqueous t e x t i l e padding bath c o n t a i n i n g trimethoxymethylmelamine, and c o t t o n f l a n n e l c l o t h was padded w i t h t h i s s o l u t i o n , d r i e d and t h e r e s i d u a l a m i n o p l a s t s c u r e d a t 177°C f o r two h o u r s , t h e f a b r i c was found t o be permanently flame r e t a r d a n t . T h i s i s i l l u s t r a t e d i n F i g . 12a, Eq. 3. An important c h a r a c t e r i s t i c o f ("lame r e t a r d e d t e x t i l e s , t h e "hand" o r f e e l o f t h e c l o t h , was s a t i s f a c t o r y ; i t d i d not become stiff. S i m i l a r r e s u l t s were o b t a i n e d when p a d d i n g c o t t o n f l a n n e l w i t h padding s o l u t i o n s c o n t a i n i n g e i t h e r d i m e t h y l (carbamoylmethy1) phosphate or methyl bis CH 0$(OCH CNH )

3

2CH OH

3

—(CH 0) POCH CNH

3

+ 2NH

2

2

2

CH |oCH ?NH

Δ

5

a)

3

+CH OH

2

—CH S(OCH 2NH )

3

2

3

CH

3.

3

(CH 0)§0CH CH.HC1

2.

2

3

2

2

2

+

5

2C H OH 2

5

F i g u r e 11. P r e p a r a t i o n o f phosphonoxy carboxamides. P o t e n t i a l flame r e t a r d a n t s f o r c o t t o n f a b r i c s ( 2 7 , 2 9 , 3 0 ) .

(CH 0) ?H 3

+ CH =CH§NH

2

2

(CH 0) ^CH CH 2NH 3

2

2

2

Ο Ο (CH 0) PCH CH CNH

2.

3

2

2

2

a)

b)

Ο O CH &OCH CNH oCHo 3

2

2

Ο Ο CH P(OCH CNH ) 3

2

2

Ο p :) ( C H 0 ) P O C H C N H 3

2

2

3

3

3

3

2

2

2

3

2

2

2

2

Catalyst ^ Aminoplast Resin

Commercial flame r e t a r d a n t f o r c o t t o n

Acid Catalyst -r ^ Aminoplast Δ Resin

[N(CH OH) ] 2

2

3

+ C N [N(CH OCH ) ] 3

+ C N 3

2

(CH 0) ^CH CH ?NH(CH OH)

2

+ C N [N(CH OH) ]

3

2

2

Acid 2

+ C N

2

2

3

+ CH 0

2

F i g u r e 12. P y r o v a t e x CP. f a b r i c s . ( 3 1 , 32, 33)

3.

>(CH 0) P^H CH CNH

2

3

3

2

3

2

[N ( C H O C H ) ] 2

3

2

3

Acid

Catalyst ^-Aminoplast Δ. Resin

Acid

Catalyst Âminoplast Δ Resin

3

F i g u r e 12a. Flame r e t a r d a n t s f o r c o t t o n f a b r i c s . ( 2 7 , 30)


20. BRIGHT ET AL


Β

&

5

1. 3 ( C H 0 ) $ C H O H

+ P0C1

2. 2 ( C H 0 ) P C H O H

+ (C H 0) #H

2

2

5

2

5

2

2

2

F i g u r e 13.

3.

2

>

3

5

2

—>

5

2

2

3

[(C H 0) PCH 0] ÊH 2

5

2

2

+ 2 C H OH

2

2

5

New p h o s p h o r u s - c o n t a i n i n g p l a s t i c s a d d i t i v e s . ( 3 5 )

( C H 0 ) J ? O H +n CÎÎ^bH

b)

6(C H 0) 5(OCH CH ) OH

5

2

[ ( C H H 0 ) ? C H 0 ] $ + 3 Base#HCl

2

a)

2

269


5

2

2

2

— ^

2

(C H 0) $(OCH CH ) OH 2

+ P O

n

4

5

2

2

2

R

— *

1 0

2[(C H 0) §(OCH CH ) O] §OH 2

5

2

2

2

n

2

+

I

2[(C H 0) ^ 2

5

2

(

O

C

H

2

C

H

2

)

n

0

^

]

(

0

H)

II

C)

I & II

+

(r+s+t)

v,n -v.n 2

2

[(C H 0) ^(OCH CH ) 0] P(OCH CH ) 0H 2

5

2

2

2

n

2

2

2

r

+ [(C H 0) §(OCH CH ) O]?--(OCH CH ) OH 2

5

2

2

2

n

2

2

s

XOCH CH ) OH 2

2

t

F i g u r e 13a. New p h o s p h o r u s - c o n t a i n i n g p l a s t i c s a d d i t i v e s . ( 3 6 )


2

270



phosphorus-containing acids I s an o f t e n used procedure i n industrial l a b o r a t o r i e s t o form n e u t r a l e s t e r s o f phosphorus a c i d s . Unfortunately, little i s p u b l i s h e d about t h e r e a c t i o n mechanism, the methods t o c o n t r o l t h e d i r e c t i o n o f t h e r e a c t i o n , t h e methods to c o n t r o l t h e p r o d u c t formed, o r t h e n a t u r e o f t h e p o l y o x y a l k y l e n e p r o d u c t s formed. Perhaps t h e a v a i l a b i l i t y o f t e c h n i q u e s such a s silination and gas chromatography w i l l encourage i n v e s t i g a t o r s t o reexamine t h i s f i e l d o f r e s e a r c h . The impure d i e t h y l hydroxyethyl phosphate was r e a c t e d w i t h phosphorus ( V ) o x i d e , a s shown i n F i g . 13, Eq. 3b, and t h e r e s u l t i n g m i x t u r e o f p h o s p h o r i c a c i d s was n e u t r a l i z e d w i t h e t h y l e n e o x i d e t o y i e l d a c l e a r , n o n - v o l a t i l e o i l w i t h a phosphorus c o n t e n t of 16.5%. The r e a c t i o n of these phosphorus a c i d s w i t h e t h y l e n e oxide i s illusrated i n Eq. 3 c . T h i s product mixture has a f u n c t i o n a l i t y s i m i l a r t o t h a t o f V i r c o l 82. One

l a s t item t h a t h a s l i t t l e t o do w i t h polymer a d d i t i v e s .

D u r i n g t h e summer o f 1981, J . L. M i l l s , o f Texas T e c h n i c a l U n i v e r s i t y , j o i n e d o u r l a b o r a t o r y f o r a summer r e s e a r c h program. One of h i s assignments was t o look a t methods f o r p r e p a r i n g phosphorus ( I I I ) o x i d e and t o conduct r e s e a r c h on t h e c h e m i s t r y o f this phosphorus oxide. In t h e c o u r s e o f t h i s work, M i l l s c o n s i d e r e d t h e u s e o f m i l d o x i d a n t s and m i l d oxidatât i o n c o n d i t i o n s for t h e o x i d a t i o n of e l e m e n t a l phosphorus. Some o f t h e o x i d a n t s he proposed o r t r i e d were t r i p h e n y l p h o s p h i n e o x i d e , d i m e t h y l s u l f o x i d e and t r i m e t h y l a m i ne o x i d e . These r e a c t i o n s a r e i l l u s t r a t e d i n F i g . 14. To my knowledge, i f he t r i e d these r e a c t i o n s he d i d not succeed i n g e t t i n g these l a t t e r t h r e e compounds t o a c t a s an oxidants f o r elemental phosphorus. However, a s he l e f t o u r l a b o r a t o r y , he suggested that iodine, since i t r e a d i l y o x i d i z e s elemental phosphorus, may a c t a s a c a t a l y s t f o r such o x i d a t i o n reactions. Many y e a r s l a t e r the attempts t o o x i d i z e elemental ( w h i t e ) phosphorus w i t h t r i p h e n y l p h o s p h i n e o x i d e and w i t h d i m e t h y l s u l f o x i d e were r e p e a t e d . I n t h e case o f d i m e t h y l s u l f o x i d e , when dimethyl s u l f o x i d e was added t o a s u s p e n s i o n o f w h i t e phosphorus i n x y l e n e and t h e system was warmed t o r e f l u x w h i l e s t i r r i n g , no evidence f o r a r e a c t i o n was o b s e r v e d ; t h e e l e m e n t a l phosphorus remained a s e p a r a t e phase. When t h i s experiment was r e p e a t e d i n the presence o f a c r y s t a l o f i o d i n e , a moderate exotherm was noted at 40-44°C, a s t h e e l e m e n t a l phosphorus m e l t e d . When t h e reaction was completed, dimethyl s u l f i d e had formed and t h e oxidized phosphorus was p r e s e n t a s a s e p a r a t e gummy phase. H y d r o l y s i s o f t h e o x i d i z e d phosphorus l e d t o a m i x t u r e o f o r t h o and p y r o p h o s p h o r i c acid. T h i s i s shown i n Eq, 2. Thus, t h e o x i d a t i o n r e a c t i o n had o x i d i z e d t h e phosphorus t o t h e p e n t a v a l e n t state. U n f o r t u n a t e l y , t h e r e a c t i o n d i d not s t o p a t t h e t r i v a l e n t s t a t e o f phosphorus. T h i s i s perhaps c o n s i s t e n t w i t h t h e f i n d i n g s of R. W. L i g h t and R. T. P a i n e ( 3 8 ) , who used s u l f u r d i o x i d e t o o x i d i z e hexamethylphosphorous t r i a m i d e t o form hexamethylphosphoric t r i ami de and reduced s u l f u r , a s shown i n Eq. 5. The s u l f u r d i o x i d e had been reduced a t l e a s t t o t h e d i v a l e n t s t a t e (and, c o n s i d e r i n g


20. BRIGHT ET Al»

1.

P

4

+

2.

P

4

+ CH SCH.

No

(C H ) PO 6

5

271


3

>

3

to

Reaction

No

Reaction

137°C H 0 2

[Ρ °1θ3 4

+

C H S C H3 3

>

3

H

H

3

P 0

4

+

P

4 2 ° 7 +CH SCH


3

3.

P

+

4.

(C H ) PO +

4

6

(CH ) NO 3

5

3

3

(C H 0) P 6

5

(C H ) P

3

6

5

3

+(C H 0) PO 6

5

3

365 C

5.

P[N(CH ) ] +S0 3

2

3

2

^ OP[N(CH ) ] 3

2

3

+ SP[N(CH ) ] 3

2

3

+

Polymeric Products

F i g u r e 14. Use of e l e m e n t a l phosphorus a s a r e d u c i n g a g e n t . (37, 38, 39, 40)

the b y - p r o d u c t , p e r h a p s o r i g i n a l l y t o the zero valent s t a t e ) . Thus, i t i s likely t h e i o d i n e r e a c t s t o form a t r i v a l e n t ( o r a t least a non-zero v a l e n t ) phosphorus i n t e r m e d i a t e , which i n t u r n i s e a s i l y o x i d i z e d t o the pentavalent s t a t e ( 4 0 ) . It i s i n t r i g u i n g to consider t h e mode of r e d u c t i o n t h a t elemental phosphorus might take i f , i n t h e absence o r p r e s e n c e of iodine, i t i s effective i n r e d u c i n g n i t r o and n i t r o s o compounds (Eq. 3 ) . What type of reduced n i t r o g e n compounds would form? A l s o , t h i s might be an e l e g a n t method f o r r e d u c i n g t h e N - o x i d e s o f heterocyclic compounds. These N - o x i d e s a r e o f t e n formed i n h e t e r o c y l i c compounds, such a s p y r i d i n e , t o a l t e r t h e o r i e n t a t i o n of s u b s t i t u t i o n . When r e a c t i o n of e l e m e n t a l phosphorus w i t h t r i p h e n y l phosphine o x i d e was t r i e d , no r e d u c t i o n o f t h e t r i p h e n y l phosphine o x i d e was o b s e r v e d a t t e m p e r a t u r e s up t o t h a t of r e f l u x i n g x y l e n e , 137 °C, w i t h o r w i t h o u t t h e p r e s e n c e o f t h e c a t a l y t i c amount o f iodine. P e r h a p s , had a h i g h e r b o i l i n g s o l v e n t been u s e d , one t h a t a l l o w e d one t o r e a c h t e m p e r a t u r e s c l o s e r t o t h o s e a c h i e v e d by J . N. Gardner and J . K o c h l i n g (39) who r e d u c e d t r i p h e n y l phosphine o x i d e to triphenyl phosphine a t 365°C, u s i n g t r i p h e n y l p h o s p h i t e a s the r e d u c i n g a g e n t , a s i m i l a r r e d u c t i o n might have been e f f e c t e d .



272


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Development of Functional Organophosphorus Compounds

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