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Isocyanates of Esters of Some Acids of Phosphorus and Silicion.

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Proof of the formation of 2,2-dimethyl-l,3-dioxolein
the ionic hydrogenation of addition product (3) with
2,2-dimethyl-1,fdioxolan :
A mixture of 12.5 g of 2,2-dimethyl-l,3-dioxolan
and 25 ml
of glacial acetic acid is added to 10 grams of addition product
(3). The mixture is then stirred and heated to 60°C. The
diazonium salt dissolves, and after 10 minutes, the reaction is
completed. After working up as described above, 89.3 % of
trimethylammonium fluoroborate and 51.9 % of 1,3,5-trichlorobenzene are obtained.
To demonstrate the presence of the 4-acetoxy-2,2-dimethyl1,3-dioxolan formed, another reaction mixture on the same
scale was treated with 2 N hydrochloric acid and 50 ml of
water; the mixture was agitated for 3 hours, and the acetone
formed removed by vacuum distillation. After filtering off the
precipitate of 1,3,5-trichlorobenzene, the filtrate was treated
with a solution of 10 g ofp-nitrophenylhydrazine in 150 ml
of 2 N hydrochloric acid. The resulting mixture was allowed
of crude
to stand for 2 days. This yielded 4.06 g (43.8
glyoxal-p-nitrophenylosazone,which, after recrystallization
from pyridine, melted at 307-312°C.
We are indebted to the Fonds der Chemie, Farbenfabriken
Bayer, and Chemische Fabrik Schering A.G. for generous
support for our work.
Received, July 31 st, 1962
[A 232152 IE]
Isocyanates of Esters of Some Acids of Phosphorus and Silicon
BY DR. H. HOLTSCHMIDT AND DR. G. OERTEL
WISSENSCHAFTLICHES HAUPTLABORATORIUM DER FARBENFABRIKEN BAYER AG.
LEVERKUSEN (GERMANY)
Dedicated to Prof. Dr. Otto Bayer on the occasion of his 60th birthday
Several aminoaryl esters of phosphoric and thiophosphoric acids were prepared by the
reaction of phosphorus pentahalides with nitrophenols, followed by catalytic hydrogenation,
or by treating aminophenols with phosphorus trihalides and oxidation to pentavalent phosphorus. These amino esters were then converted into isocyanato esters by the action of
phosgene. Isocyanates of phosphonates have been synthetized on the same principle, as well
as via the Arbusov reaction of halogen-substituted isocyanates with trialkyl phosphites. The
reaction of silicon halides or alkylhalogenosilanes with aminophenols yielded aminoat-yI
esters of silicic acid or its derivatives, which could also be treated with phosgene to convert
them into isocynnato esters.
1. Introduction
The preparation of isocyanates bearing an ester group
in the molecule was described in 1906 by Morel El], who
used phosgenation of the hydrochloride of ethyl aminoethanoate to form ethyl isocyanatoacetate ( 1 ) as an
example. Siefken and Petersen 121 later prepared isocyanates from esters of other aliphatic and aromatic
amino acids, such as ethyl E-isocyanatohexanoate and
v
H~C~+C-CHZ-NCO
(I)
p-ethoxycarbonylphenyl isocyanate, while Miiller et
al. [3] synthetized higher functional isocyanate esters,
e.g. the bis-m-isocyanatobenzoateof diethylene glycol
(2). Isocyanato esters with polymenzable groups, e.g.
(3-isocyanatoethyl acrylate and methacrylate (3), have
also become known as the result of recent investigations [4].
We have been occupied for some time with the preparation of isocyanates of esters of inorganic acids; this work
will be discussed in the following.
A. Isocyanates of Esters of Phosphorus Acids
I. Isocyanates of Phosphates and Thiophosphates
OCN'
NCO
[I] A. Morel, C. r. hebd. Seances Acad. Sci. 143, 119 (1906).
[2] A. Siefken and S . Petersen, Liebigs Ann. Chem. 562, 75
(1949).
Angew. Chem. internat. Edir. / Vol. I (1962) / N o . 12
Nitration of triphenyl phosphate with concentrated nitric
acid yields tris-(p-nitrophenyl) phosphate (4), which
can easily be hydrogenated with Raney nickel to give
[3] German Pats. 1078 115 (Dec. 13th, 1957), 1081667 (April 4th,
1959), and 1085869 (Dec. 16th, 1959); inventors: E. Miiller,
0. Bayer, H. Wilms, F. v. Spulak, and M. Theis.
[4] German Pat. 1018050 (April 26th, 1954); inventor: H. HaltSchmidt.
617
tris-(p-aminophenyl) phosphate (5). Upon treating the
latter with phosgene, tris-(p-isocyanatophenyl)phosphate (6) is obtained.
‘[.GNOJ
H2”iw
50°C
3
(4) 8 5 %
r
r
The ease of hydrogenation [5] of the trinitro compound to
the triamine (5) is surprising. Amidation or saponification of
the ester groups by water formed during hydrogenation does
not occur.
N,N-dimethylphosphoramidic dichloride, the phosphoramidic esters (9) and (10) are obtained in very good
yields, following the synthesis principle mentioned
above. While the bis-(p-aminopheny1)-N-methyl-Nphenylphosphoramidate (9) is easily converted by phosgenation into the expected diisocyanate ( I I ) , the N,Ndimethyl derivative (10) undergoes cleavage under these
conditions, resulting in N,N-dimethylcarbarnyl chloride
and the diisocyanate ester derivative of phosphorochloridic acid (12).
The favorable results obtained with the hydrogenation
of nitrated phosphoric esters and the phosgenation of
amines encouraged us to attempt the corresponding
reactions with thiophosphates. Surprisingly, it was found
that hydrogenation over Raney nickel of 0,O-diethylp-nitrophenyl thiophosphate (“E 605”) [7] (13) was possible, giving a yield of more than 90 %.
The phosgenation 161 of the amine (5), which gives the
tri-isocyanate (6) in a high yield, indicates the stability
of aromatic phosphoric ester bonds toward phosgene
and hydrogen chloride, at temperatures up to 150°C.
By analogy, monophenyl-bis-(p-aminophenyl)phosphate (7) can be converted with phosgene into the diisocyanate (8), without cleavage of the ester bond.
+2
@-!Czl
HO
eNo2
1. NaOH(8OI)
2. H2/Ni(90%)
The 0,O-diethyl-p-aminophenyl
thiophosphate (14)obtained in the hydrogenation reacts easily with phosgene,
yielding the isocyanate (15).
The preparation of the tris-(p-isocyanatophenyl) thiophosphate (16) succeeds particularly well:
(71
w
PC13 + 3 HO
eNoz
-
1. NaOH(SO%)
2. Hz/Ni(96%))
97%
Esters of phosphoramidic acid are however not always
stable towards phosgene. For example, starting from
N-methyl-N-phenylphosphoramidic
dichloride, or from
(9)
This triisocyanate is suitable as a glue for rubber adhesive
solutions, and has been o n the market since 1959 under the
name “Desmodur m~ RF” [8,9]. Compared with tri-(p-isocyanatopheny1)methane (“Desmodur R”) [gal, besides having
equal adhesive strength, it has the advantage of being colorless; “Desmodur R” has a n intense violet color, which is a
disadvantage in the cementing of light colored, or transparent
materials.
95%
88%
During the further course of our attempts to synthetize
isocyanates of phosphoric and thiophosphoric esters,
we investigated the reaction between phosphorus halides
and amino phenols, as well as amino-alcohols. Chlorides
of pentavalent phosphorus, i.e. phosphorus oxychloride
and phosphorus sulfochloride, react with aminophenols,
~
[ 5 ] German Pat. 1085869 (Feb. lst, 1958); inventors: H. HolrSchmidt and H. Wilms.
[6]Belg. Pat. 575407 (Feb. 6th, 1958); inventor: H . Holtschmidt.
618
[7] German Pat. 763 153 (Aug. lst, 1938); inventors: G. Schrader and H . Kiikenthal.
[8] Belg. Pat. 576226 (March lst, 1958); inventors: H. HoltSchmidt, F. v. Spulak, E. Miiller, and 0. Bayer.
191 German Pat. 1092190 (March 22nd, 1958); inventors: H.
HoItschmidt and G. Braun.
[9a] German Pat. 585902 (March 5th, 1942); inventors: S.
Petersen, H. Kleiner, and F. v. Spulak.
Angew. Chem. internal. Edit.
Yol. I (1962) / No. I2
giving nonuniform products which contain aminophenyl
ester groupings, as well as hydroxyphenylamido groupings. They therefore show a behaviour similar to carbonyl chlorides, or sulfonyl chlorides.
In contrast, the reaction of the trivalent phosphorus
halides with aminophenols [lo] takes place in an unexpected and uniform manner. For example, the reaction of phosphorus trichloride with m-aminophenol in
toluene or chlorobenzene gives a nearly quantitative
yield of the tris-(m-aminophenyl) phosphite hydrochloride, from which the free base (17) can be obtained
by treatment with dry ammonia gas. The aminoaryl
phosphites (18) through (20) are obtainable in a
similar way. Overall yields: (17) 95 %, (18) 30 %, (19)
96 %, and (20) 70 %.
formed is then easily converted with phosgene into the
bis - (3 - isocyanato - 4- methylphenyl) styrylphosphonate
(Z),following the usual process [13].
1
hco J,
2. Isocyanates of Phosphonates from a-Halogenoalkylaryl Isocyanates and Triaikyl Phosphites
Isocyanates containing phosphonic ester groupings
were prepared by us in a very simple manner from
phosphorus-freepolyisocyanates and trialkyl phosphites,
by using the Michaelis-Arbusov reaction.
1
Direct conversion of these aminoaryl esters into isocyanato esters is not possible, owing to simultaneous
cleavage of the ester groups. The aminoaryl phosphites
can, however, be converted with oxygen or sulfur into
the aminoaryl phosphates or thiophosphates, respectively [ll], which, as described above, react readily with
phosgene, giving isocyanato esters [*I.
11. Isocyanates of Phosphonates
1. Isocyanates of Phosphonafes from Phosphonic
Dihalides
The reactions described in the previous section of nitroand aminophenols with phosphorus halides permit the
preparation of isocyanatesof phosphonic and phosphinic
esters, when applied to phosphorus halides in which one
or two hydrocarbon groupings are linked to the phosphorus. From the vast number of isocyanato esters thus
available onIy the unsaturated isocyanato phosphonate
(22) will be described. Styrylphosphonic dichloride
(21), obtained from styrene and phosphorus pentachloride [12], reacts with 3-amino-4-methylphenol like
a trivalent phosphorus halide, although it is a pentavalent phosphorus compound. The aminoaryl ester
[lo] German Pat. Appl. F 28 607, IVbl120 (June 4th, 1959); inventors: G. Oertel and H . Holtschmidt.
[*I Halides of trivalent phosphorus react uniformly with aliphatic amino alcohols, too. However, the conversion of the
aminoalkyl phosphites into isocyanates presents difficulties.
[ l l ] German Pat. Appl. F 29 199, IVb/l20 (Aug. 18th, 1959);
inventors: G. Oertel and H. Holtschmidt.
[12] K. N. Anisimov, Izvest. Akad. Nauk S.S.S.R., Otdel. Khim.
Nauk 1954,796; Chem. Abstr. 49, 13074 (1955).
Angew. Chem. internat. Edit. / Yo[.I (1952) No. I2
u-Halogenoalkylaryl isocyanates have been easily available
since 1953 [14]. We tried to obtain isocyanato phosphonic
esters (24) for example by reacting 2,4-diisocyanatobenzyl
chloride (23) with trialkyl phosphites; these attempts failed,
however. It could only be ascertained that the MichaelisArbusov reaction is possible at approximately 140 "C, whereby alkyl halide is split off. However, a concurrent polymerization of the NCO groups takes place, under the influence
of the trialkylphosphite.
s
CHzCl
NCO
NCO
J.
0"""
NHCOSR
(251
R'(26)
We then found that by simultaneousaction of equimolar
amounts of triaIky1 phosphite and alcohol on the diisocyanatobenzyl chloride (23), the chlorine atom is
loosened to such an extent [*I by the basic urethane
group originating, that it reacts with the trialkyl phosphite even at room temperature. The reaction under
these conditions proceeds without simultaneous polymerization of the NCO groups, yielding phosphorylated
monoisocyanates(25) with alcohols, and phosphorylated
polyisocyanates, e.g. (26) with di- or polyols.
[13] German Pat. Appl. F 30 748, IVbll20 (March 12th, 1960);
inventors: G. Oertel and H. Holtschmidt.
[I41 German Pat. 947470 (April loth, 1953); inventor: HAHoltSchmidt.
[*I See H. Holtschmidt, Angew. Chem. internat. Edit. I , 632 (1962).
619
3. Isocyanates of Carbamylphosphonates from Isocyanatocarbamyl Chlorides and Trialkyl Phosphites
ous Sections 11, 2-4 are of interest in the manufacture
of fire-resistant polyurethane plastics [20-221.
Mono- and dialkylcarbamyl chlorides react with trialkyl phosphites even under exceptionally mild conB. Isocyanates of Esters of Silicic Acid
ditions, giving carbamylphosphonic esters [15, 161.
and its Derivatives
This reaction can be applied to isocyanatocarbamyl
chlorides : The isocyanatocarbamyl chloride (27), obtained from tolylene-2,4-diisocyanateby the action of
The strange reaction of trivalent phosphorus halides
equimolar quantities of hydrochloric acid, easily reacts
with aminophenols and aminoakohols has prompted us
with trialkyl phosphites even at room temperature to
to react silicon halides with aminohydroxy compounds.
yield 3-isocyanato-4-rnethylphenylcarba~Y~P~~~P~~~~~
In this way, it is in fact possible to prepare aminoaryl
esters (28).
and aminoalkyl esters of silicic acid and its derivatives.
For example, silicon tetrachloride and m-aminophenol
react easily to give the hydrochloride of tetra-(m-aminophenyl) silicate (32), while the hydrochloride of the
silanol etheramine (34) is formed from dimethyldichlorosilane and ethanolamine.
CH3
r
4. Isocyanates of Phosphonates from Trialkyl Phosphites
and Chloroformylchloroformamidines containing NCO
Groups
-l
I
-NH4C1 +NH3
The addition of phosgene onto isocyanates containing
carbodiimide groups has become known through the
works of P. Fischer [17, 181. The addition products are
isocyanates with N-chloroformylchloroformamidine
groups, and react with trialkyl phosphites even under
very mild conditions, giving isocyanato phosphonic
esters [19], in the same manner as the isocyanatocarbamyl chlorides described in Section 11, 3. The carbodiimide (29), obtained from tolylene-2,4-diisocyanate
(34)
+ NH3
-N&C1
(35)
To isolate the free bases (33) and (35), it is generally
sufficient to saturate the suspension of the hydrochlorides with gaseous ammonia in an inert solvent, e.g.
toluene or chlorobenzene. Ammonium chloride precipitates; the free amine can be isolated from the
filtrate. The yields are mostly over 90 %.
(30)
+ P(0R)s
-
RC1
~~
OCN
I
{(OR),
0
Nco
(31)
adds on phosgene and forms the N-chloroformylchloroformamidine (30), which can be treated with trialkyl
phosphites to give isocyanato phosphonic esters (31).
The isocyanato phosphonic esters described in the previ[IS] T. Reetz, D. H . Chadwick, E. Hardi, and S. Kaufmann, J.
Amer. chem. SOC. 77, 38 13 (1955).
1161 B. A. Arbusov and N. I. Rizpolozhenskii, Izvest. Akad. Nauk
S.S.S.R., otdel. Khim. Nauk 1952, 847; Chem. Abstr. 47,
1045711 (1953).
[17] German Pat. Appl. F 32 656, IVb/120 (Nov. 30th, 1960);
inventor : P. Fischer.
[IS] German Pat. Appl. F 32 487, IVb/l20 (Nov. 5th, 1960);
inventor: P. Fischer.
[19] German Pat. Appl. F 32 903, IVb/I20 (Jan. 5th, 1961);
inventors: G. Oertel, H. Holtschmidt, and P. Fischer.
620
[20] Belg. Pat. 607180 (Aug. 25th, 1960); inventors: G . Oertel,
H . Holtschmidt, G. Nischk, and G. Braun.
I211 German Pat. Appl. F 32 636, IVb/l20 (Nov. 26th, 1960);
inventors: H . Holtschmidt, E. Deganer, and G. Braun.
[22] German Pat. Appl. F 34 008, IVb/39b (May 25th, 1961);
inventors: P . Fischer, H . Holtschmidt, G . Oertel, and G . braun.
Angew. Chem. internat. Edit. / Vol. I (1962) f No. 12
These amines react very differently with phosgene.
While the silicates or silanol ethers of aliphatic aminoalcohols, such as (35), are completely cleaved, even
under extremely mild conditions, the esters or silanol
ethers of aminophenols, e.g. (33), can be easily converted
isocyanates, starting with either the
chloride or the free base. w e have thus been able to
obtain the isocyanato esters (36) through (39) analytically pure without difficulties [23].
Silicones containing aminophenyl terminal groups can
be converted into isocyanates in the same manner.
Received May 23rd, 1962
[A 242159 IE]
,231 German pat. 1066582 (Oct. 31st, 1958); inventors: H. Ho[tand 0,Bayer.
The Preparation of Carbodiimides from Isocyanates
BY DR. W. N E U M A ” AND DR. PETER FISCHER
WISSENSCHAFTLICHES HAUPTLABORATORIUM AND Z W I S C H E N P R O D U K T E - A B T G ,
FARBENFABRIKEN BAYER A.-G., LEVERKUSEN (GERMANY)
Dedicated to Prof. Dr. Otto Bayer on the occasion of his 60th birthday
Carbodiimides are formed with simultaneous evolution of C02 by the reaction of basic
catalysts with sterically hindered isocyanates. Another generally applicable synthesis of
carbodiimides involves intermediate formation of cyclic adducts of isocyanates and carbodiimides, which, upon cleavage, exchange the isocyanate and carbodiimidefunctions. Both
processes are suitable for the preparation of polycarbodiimides. Several commercial applications of mono- and polycarbodiimides are pointed out.
1. Carbodiimides
from Sterically Hindered Isocyanate
Introduction
The formation of carbodiimides [l] on heating isocyanates has been known for a long time [2]. It takes
place formally according to the equation :
2 R-NCO + R-N=C=N-R
+ CO2.
This reaction achieved general and commercial applicability only in recent years when catalysts were found
which can greatly accelerate it. Phospholenes (I) and
phospholanes (2) as well as their oxides and sulfides (3)
aad (4) [3] provide such a catalytic effect.
Derivatives of isocyanuric acid [ 5 ] are generally formed
from isocyanates in exothermic reactions under the
inflrlence of strongly alkaline catalysts. Carbodiimides
are formed from sterically hindered isocyanates, that is,
isocyanates containing bulky groups in positions adjacent to the NCO group, under the influence of these
same catalysts [6]. We studied this reaction first on
aromatic o-alkyl monoisocyanates [7], which were
prepared by the reaction of the corresponding amines
with phosgene [8]. Effective catalysts for the formation
of carbodiimides from such isocyanates are basic compounds usually used for trimerizations such as alcoxides, alkali carbonates, alcoholic sodium or potassium hydroxide, or tertiary amines. Heavy metal salts
of carboxylic acids, such as lead octoate, tin(I1) octoate, lead and cobalt naphthenates [9], dibutyltin
A few years ago, we found that simple phosphine
oxides, such as tributyl-, triphenyl-, tribenzyl-, phenyldibutylphosphine oxide, etc., also react, though less
vigorously, with isocyanates to form carbodiimides [4].
[l] Review: H. G. Khorana, Chem. Reviews 53, 145 (1953).
[2] A . W . Hofmann, Ber. dtsch. chem. Ges. 18, 765 (1885); R.
Stolle, ibid. 41, 1125 (1908).
[31 T. W. Campbell and J. J. Verbanc, US.Pat. 2853473 (1956/
1958); W.J. Balon, U.S.Pat. 2853518 (1956/1958). Compounds
(I) and (2) are frequently called phospholines and phospholidines, respectively.
141 After the conclusion of our work, we found in a conference
report (Angew. Chem. 74, 127 (1962)] the statement that T. W.
Campbellalso observed the catalytic effect of non-cyclic phosphine
oxides during the formation of carbodiimides from isocyanates.
Angew. Chem. internat. Edit. 1 Vol. I (1962) / No. 12
[5] A . W. Hofmann, Ber. dtsch. chem. Ges. 18,764 (1885); see also
J. H , Snunders and R . J. Slocombe, Chem. Reviews 43,203 (1948).
[6] The process is the subject of patents and patent applications,
see e. g. W. Neumann, French Pat. 1293252 (1961/1962).
[7] Aromatic 0-alkylamines are easily accessible by the reaction
of olefins with aromatic amines: R. Stroh et al., Angew. Chem.
69, 124 (1957).
[8] We thank Dr. W. Siefken (Wissenschaftliches Hauptlaboratorium der Farbenfabriken Bayer AG.) for the preparation of
several isocyanates used in this work.
[9] According to a paper published after our patent application,
carbodiimides are formed, in addition to derivatives of isocyanuric acid, by the reaction of metal naphthenates and atuminum isopropoxide with I-naphthylisocyanate and diphenylmethane - 4,4‘- diisocyanate: E. Dyer and E . E. Rend, J. org.
Chemistry 26, 4677 (1961).
621
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