Flame retardant properties of phosphorylated derivatives of malonic ester

Article abstract of DOI:10.1134/S1070363213040087

Thermal stability of the phosphorylated derivatives of malonic ester synthesized by the Michaelis-Becker reaction was studied. The flame-retardant efficiency of the phosphonomalonic ester was assessed by the flame-tube technique measuring the weight loss of wood samples impregnated with the studied compound.

Full text of DOI:10.1134/S1070363213040087

ISSN 1070-3632, Russian Journal of General Chemistry, 2013, Vol. 83, No. 4, pp. 659–662. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © L.K. Sal’keeva, E.K. Taishibekova, E.V. Minaeva, A.K. Shibaeva, R.Z. Kasenov, A.K. Sal’keeva, A.A. Muratbekova, 2013, published
in Zhurnal Obshchei Khimii, 2013, Vol. 83, No. 4, pp. 571–574.
Flame Retardant Properties of Phosphorylated Derivatives
of Malonic Ester
L. K. Sal’keeva, E. K. Taishibekova, E. V. Minaeva, A. K. Shibaeva,
R. Z. Kasenov, A. K. Sal’keeva, and A. A. Muratbekova
Buketov Karaganda State University, ul. Universitetskaya 28, Karaganda, 100028 Kazakhstan
e-mail: LSalkeeva@mail.ru
Received March 19, 2012
Abstract―Thermal stability of the phosphorylated derivatives of malonic ester synthesized by the Michaelis–
Becker reaction was studied. The flame-retardant efficiency of the phosphonomalonic ester was assessed by the
flame-tube technique measuring the weight loss of wood samples impregnated with the studied compound.
DOI: 10.1134/S1070363213040087
Earlier we showed [1] that the reaction route of
bromomalonic ester with sodium diethyl phosphite by
the Michaelis–Becker reaction scheme was strongly
dependent of the order of mixing and degree of
dilution of the reagents. When a benzene solution of
sodium diethyl phosphite was slowly added to
bromomalonic ester, NaBr precipitation was observed;
after its separation diethyl (diethoxyphosphinoyl)
malonate (I) was isolated by distillation. A little
tetraethyl ethylenetetracarboxylate (II) was isolated as
a by-product, white crystals, mp 55–56°С (published
data: mp 53–54°С). With stronger diluted reagent
solutions, ester II hardly formed.
If the reagents were mixed in the reverse order
strong heat release was observed and NaBr
precipitated; after separation of the NaBr precipitate,
ester II precipitated as white crystals, mp 55–56°С.
Distillation of the mother liquor gave diethyl hydrogen
phosphite (III).
O
(
EtOOC) CH P(OEt)2
2
I
(
EtOOC) CHBr + (EtO) PONa
2
2
−
NaBr
(
EtOOC) C=C(COOEt) + (EtO) PHO
2
2
2
II
III
The IR spectrum of compound I contains absorp-
To confirm the structure of compound I we
tion bands characteristic of the C=O group at 1744 and
performed its reaction with urea and isolated phos-
phonobarbituric acid IV, mp 97°С, whose parameters,
too, were consistent with published data [2].
–1
–1
1
731 cm and a Р=О band at 1202 cm , which is
consistent with published data [2].
O
O
C
C
NH
NH
I + H N
C
NH2
(EtO)2P CH
C
O + 2EtOH
2
O
O
IV
659

6
60
SAL’KEEVA et al.
Ester I was further subjected to chemical modifica-
retardant properties of phosphites and phosphonates, as
well as amides of phosphonic acids have scarcely been
studied [3].
tion to prepare diamides. The latter may be interesting
for practical applications, in particular, as flame
retardants.
Aiming at a search for new flame retardants and
assessing their efficiency, we chose as objects for the
study phosphonomalonic diamide V and full amide of
ethylenetetracarboxylic acid VI.
(
Diethoxyphosphinoyl)malonic diamide (V) was
synthesized in high yield by the ammonolysis of ester I
with an excess of aqueous ammonia.
O
The efficiency of the potential flame retardants for
wood was assessed according to State Standard 16363-
76 (Comecon Standard 4686-84) by a procedure
involving measurement of the weight loss of wood
samples treated with impregnating compositions in
flame resistance tests and comparison of the results
with those for untreated samples.
O
NH OH
C
NH2
4
I
(EtO)2P CH
−2EtOH
C
O
NH2
V
By the same procedure we prepared enthylene-
tetracarboxylic acid tetramide (VI) which was used as
reference in the thermal stability study on organo-
phosphorus compounds V.
Impregnating compositions containing 5% solu-
tions of compounds V and 5 or 10% solutions of
compound VI were applied on all sides of dry and
weighed samples (three tests for each impregnating
solution). The concentrations were chosen taking into
account that our goal was to find an optimal flame-
retardant agent efficient at as low concentrations as
possible. The concentrations of known and widely
used flame-retardant solutions are generally no higher
than 50%. Use of more concentrated flame-retardant
solutions is economically inexpedient, since it hinders
drying of objects and deteriorates their performance
characteristics and increases toxicity.
O
O
C
NH OH
NH2
NH2
C
NH2
NH2
4
II
C
C
−
4EtOH
C
O
C
O
VI
As known, over the past years the problem of
imparting fire-retardant properties to materials of
different nature and uses is gaining in importance. This
is due to the fact that various materials are hazardous
during fires, since they are flammable, favor fire
propagation, and release much smoke and gases.
The known solvents for impregnating solutions are
water, ethanol, benzene, diethyl ether, etc. We
dissolved compound V in distilled water and
compound VI in benzene. The choice of solvents was
motivated by their chemical inertness with respect to
the solutes, as well as accessibility.
Even though at present a wide range of flame
retardants is available, including nitrogen-, phos-
phorus, and halogen-containing organic and inorganic
compounds, yet they are unable to meet all demands of
vigorously developing industry. This encourages
further R&D and implementation of fire-retardant
means, among which a particular place belongs to
organophosphorus compounds.
The treated samples were dried for 21 days until
complete dryness. After exposure to flame, untreated
wood samples lost their shape completely, whereas the
wood samples treated with impregnating solutions
completely or partially retained the shape.
Traditionally, wood and other cellulose materials
are the most widespread building materials. But,
although a number of advantages sets them apart from
other building materials, wood and cellulose materials
have certain drawbacks, the main of which are easy
ignitability and flammability. One of the most efficient
ways of flame protection of wood and cellulose
materials is their impregnation with flame retardants.
The flame-retardant efficiency was estimated from
the weight loss of a sample after exposure to flame,
using the following formula:
1 2 1
m = [(m – m )/m ]×100.
Here m is the sample weight before test, g, and m ,
1
2
sample weight after test, g.
Phosphorous acids and their esters and amidoesters
are highly reactive compounds which present both
practical and theoretical interest. However, the flame-
The result was taken as an arithmetic mean of three
test runs for each compound. The resulting data are
listed in the table.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 83 No. 4 2013

FLAME RETARDANT PROPERTIES OF PHOSPHORYLATED DERIVATIVES
Weight losses of treated and untreated wood samples
661
Sample weight be- Sample weight after Sample weight after
Compound no.
Weight loss, %
fore impregnation, g
impregnation, g
combustion, g
VI
1.651
1.735
1.652
1.657
1.891
1.848
1.523
1.780
1.712
1.972
–
1.015
0.981
0.979
1.349
1.331
1.125
0.913
0.835
0.991
0.790
0.709
0.556
41.5
41.0
27.7
49.1
59.3
1
1
.583
.585
40.6
40.9
28.7
27.9
26.1
48.7
48.8
49.7
58.7
58.9
60.2
a
V
1.831
1
1
.784
.483
b
VI
1.663
1
1
.592
.846
Untreated sample
1.912
1
1
.726
.397
–
–
a
b
Concentration in the impregnating solution, %: 5. Concentration in the impregnating solution, %: 10.
3
1
According to the above-mentioned standards, if the
0.2 ppm). The Р NMR spectra were obtained on a
Bruker АС-200 spectrometer (80.014 MHz) in CDCl3.
The melting point was determined on a Boetius heating
block (measurement error ±0.1°С). The reaction
progress and product purity were controlled by TLC on
Silufol UV-254 plates in benzene−ethanol, 6:1. The
chromatograms were developed in iodine vapor.
weight loss is less than 9%, the substance is related to
group I efficiency flame retardants providing produc-
tion of nonflammable wood. If the weight loss is more
than 9% but less than 30%, the substance is related to
group II efficiency flame retardants providing produc-
tion of nonflammable wood. If the weight loss is equal
to or more than 30%, the substance is considered as
not providing protection from flame (group III).
Diethyl (diethoxyphosphinoyl)malonate (I). а.
Sodium diethyl phosphite, 16.0 g (0.1 mol) was added
dropwise with stirring to 23.9 g (0.1 mol) of diethyl
bromomalonate in benzene. The NaBr precipitate that
formed was filtered off, and the residue was distilled in
a vacuum. Yield 25.8 g (87%), bp 159–160°С
Compound VI, with which the weight loss was
more than 30%, should be related to the III group. This
compound at chosen concentrations proved to be an
inefficient flame retardant.
2
0
(
(
1
10 mm), n 1.4457 {published data: bp 160–161°С
D
The weight loss for the wood sample impregnated
with a solution of compound V was less than 30%,
which allows it to be related to the II group.
2
0
–1
10 mm), n 1.4420 [2]}. IR spectrum (KBr), ν, cm :
D
1
202 (Р=О), 1744, 1731 (С=О). Н NMR spectrum
(
CDCl ), δ, ppm: 1.371 t (СН СН , J 7.2 Hz), 1.20 t
3
3
2
HH
Thus, our search for new cheap and sufficiently
efficient organophosphorus flame retardants resulted in
the synthesis of compound V in very mild conditions
and with an almost quantitative yield.
(
7
(
СН СН OP, J 7.2 Hz), 4.18 q (СН СН OOC, J
3 2 HH 3 2 HH
.2 Hz), 4.08 q (СН OP, J 7.2, J 14.4 Hz), 3.97 d
2 HH HР
3
1
СНР, JHР 20.5 Hz). NMR spectrum Р: δ 12.81 ppm.
P
b. Diethyl bromomalonate, 23.9 g (0.1 mol), was
added dropwise to 16.0 g (0.1 mol) of sodium diethyl
phosphite under constant stirring. The NaBr precipitate
that formed was filtered off. As the solvent was
distilled off, compound II precipitated as white
crystals, mp 55–56°С (published data: mp 53–54°С).
EXPERIMENTAL
The IR spectra were measured on a Nicolet Avatar-
60 spectrometer in pellets with KBr (measurement
error 0.2 cm ). Н NMR spectra were obtained on a
Bruker DRX500 spectrometer (500 MHz) in CDCl3
relative to internal TMS (measurement error ±0.1–
3
–1
1
–
1
IR spectrum (KBr), ν, cm : 1737 (С=О), 1627 (C=C),
1
1147 (C–O). NMR spectrum Н (CDCl ), δ, ppm: 1.37 t
3
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 83 No. 4 2013

6
62
SAL’KEEVA et al.
–
1
(
СН СН , J 7.0 Hz), 4.22 q (СН СН , J 7.0 Hz).
124–125°С. IR spectrum (KBr), ν, cm : 1693, 1670
3
2
HH
3
2
HH
1
Acid III was isolated from the residual mother liquor,
bp 80–81°С (10 mm), n 1.4072, d4 1.0714 (pub-
lished data: bp 72–73°С (9 mm), n 1.4086, d4
1
(С=О), 1263 (Р=О), 3391, 3651 (NH ). Н NMR spec-
2
2
0
20
trum (CDCl ), δ, ppm: 1.18 t (СН СН , J 7.4 Hz),
D
3
3
2
HH
2
D
0
20
3.22 d (СНР, JHР 20.8 Hz), 4.06 q (СН OP, J 7.4,
2 HH
31
31
.0742. Р NMR spectrum: δ 8.149 ppm.
J
HР 14.0 Hz), 5.46 br.s (NH
). Р NMR spectrum: δ
2 P
P
14.02 ppm.
5
-(Diethoxyphosphinoyl)barbituric acid (IV).
Urea, 6.0 g (0.1 mol), and 29.6 g (0.1 mol) of com-
pound I were added to a solution of 0.3–0.4 mol of
sodium ethylate in 20–30 ml of anhydrous ethanol.
The reaction mixture was heated under reflux for 6–
Ethylenetetracarboxylic acid tetraamide (VI).
Compound II, 31.6 g (0.1 mol), and 56.0 g of 25%
aqueous ammonia were placed in a flask. The reaction
mixture was stirred for 0.5 h under cooling and then
left to stand for 1 h until crystals formed. The crystals
7
h. Sodium barbiturate that was dissolved in water,
and the solution was acidified with dilute HCl. The
crystals that formed were recrystallized from ethanol.
Yield 22.4 g (85%), mp 97°С (published data: mp 97°С
were filtered off and dried to constant weight. Yield
–1
1
1
6.6 g (83%), mp 70°С. IR spectrum (KBr), ν, cm :
627 (С=С), 1720 (С=О), 3392, 3655 (NH2).
–
1
[
1
2]). IR spectrum (KBr), ν, cm : 1174 (Р=О), 1740,
1
628 (С=О), 3435 (NH). Н NMR spectrum (CDCl ),
3
REFERENCES
δ, ppm: 1.191 t (СН СН , J 6.8 Hz), 3.84 d (СНР,
3
2
HH
JHР 20.4 Hz), 4.19 q (СН OP, J 6.8, JHР 14.0 Hz),
2
HH
1. Sal’keeva, L.K., Tayshibekova, E.K., Nurmaganbeto-
va, M.T., Minaeva, E.V., Shibaeva, A.K., and
Sal’keeva, A.K., Zh. Obshch. Khim., 2011, vol. 81,
no. 10, p. 1746.
31
8
.33 br.s (NH). Р NMR spectrum: δ 14.01 ppm.
P
(
Diethoxyphosphinoyl)malonic diamide (V). To
2
2
9.6 g (0.1 mol) of compound I was added 28.0 g of
5% aqueous ammonia. The reaction mixture was
2
. Pudovik, A.N. and Moshkina, T.M., Zh. Obshch. Khim.,
957, vol. 27, no. 6, p. 1611.
1
stirred for 24 h at room temperature till crystals
precipitated which were filtered off and dried at 50–
3. Sultanov, M.T., Sadykov, M. M. Muratova, U.M., and
8
0°С till the constant weight. Yield 18.8 g (79%), mp
Takhtaganova, D.B., Khim. Drev., 1986, no. 5, p. 35.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 83 No. 4 2013