Organic compounds -- part of the class 532-570 series – Organic compounds – Four or more ring nitrogens in the bicyclo ring system
Reexamination Certificate
2002-11-26
2004-05-18
Ramsner, Robert W. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Four or more ring nitrogens in the bicyclo ring system
C558S074000
Reexamination Certificate
active
06737526
ABSTRACT:
BACKGROUND OF THE INVENTION
U.S. Pat. No. 4,454,064 discloses a method for preparing pentaerythritol phosphate, which comprises reacting pentaerythritol with POCl
3
in dioxane solvent at 75-125° C. The pentaerythritol phosphate thus prepared can be used as an intermediate for synthesizing a polyurethane flame retardant and a plasticizer. This preparation method will also generate HCl gas and a residual solution of excessive POCl
3
.
U.S. Pat. No. 4,478,998 discloses a synthesis of an amino-s-triazine salt of a phosphoric acid having the following formula:
when X and X′ in the formula are amino, said salt is melamine salt of bis-(pentaerythritol phosphate) phosphoric acid. The synthesized amino salt can be used as a flame retardant additive for certain polymer compositions. In Example 1 of said patent, melamine reacts with acid chloride of bis-(pentaerythritol phosphate) phosphoric acid in water to obtain said melamine salt. Said acid chloride of bis-(pentaerythritol phosphate) phosphoric acid is synthesized through the following reaction formula:
HCl gas and a residual solution of excessive POCl
3
will also be generated in the abovementioned reaction.
SUMMARY OF THE INVENTION
The present Invention provides a method for preparing a melamine salt of bis-(pentaerythritol phosphate) phosphoric acid, which comprises preparing bis-(pentaerythritol phosphate) phosphoric acid, and reacting melamine with the obtained bis-(pentaerythritol phosphate) phosphoric acid to form a melamine salt thereof. The preparation of bis-(pentaerythritol phosphate) phosphoric acid according to the present invention has the following characteristics:
1. The method uses P
2
O
5
as a reactant.
2. The method uses a mechanochemical synthesis and uses a ball mill as a reactor.
3. The method uses an alkyl benzene, such as toluene or xylene, as a solvent. The alkyl benzene may have one or two identical or different alkyls having 1 to 5 carbons.
4. The solvent used in the method is at room temperature or pre-heated to 50-150° C.
5. The method uses metal halide MX
2
, such as MgCl
2
etc., as a catalyst, wherein M=Mg, Zn, or Al; and X=Cl, or Br. The weight ratio of the catalyst to pentaerythritol is 1:99 to 5:95.
Compared to the conventional process, the present invention has the following three advantages: (a) no generation of waste gas of HCl; (b) free of a waste aqueous solution generated from neutralization of HCl waste gas; and (c) avoiding handling of a residue solution containing unreacted POCl
3
.
The reaction between melamine and bis-(pentaerythritol phosphate) phosphoric acid according to the present invention can be carried out in a ball mill or a conventional mechanical agitation reactor, which comprises ball-milling or mechanically mixing a mixture of melamine, bis-(pentaerythritol phosphate) phosphoric acid, and a solvent at room temperature to 100° C. Suitable solvents include (but not limited to) water, acetonitrile (CH
3
CN), and a mixture of the solvent used in the preparation of bis-(pentaerythritol phosphate) phosphoric acid with acetonitrile. Preferably, said solvent is pre-heated to 50-100° C. and thus there is no heating while ball milling said mixture. More preferably, said solvent is a mixture of toluene with acenonitrile preheated to 50-80° C., acetonitrile that has been pre-heated to 80° C. or boiling water, most preferably is boiling water.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
The present invention discloses a method for preparing melamine salt of bis-(pentaerythritol phosphate) phosphoric acid, which comprises preparing bis-(pentaerythritol phosphate) phosphoric acid, and reacting melamine with the obtained bis-(pentaerythritol phosphate) phosphoric acid to form a melamine salt thereof. Several factors affecting the synthesis of said bis-(pentaerythritol phosphate) phosphoric acid are discussed in the following:
1. Study on the Reaction Solvent
The molecular structure unit of phosphorus pentoxide is P
4
O
10
, usually represented by P
2
O
5
. Phosphorus pentoxide is a very strong dehydration agent, and is liable to react with water to form phosphoric acid.
P
2
O
5
+3H
2
O→2H
3
PO
4
Furthermore, it can grab H
2
O from reactant molecules to form metaphosphoric acid and related inorganic or organic material, e.g.
P
2
O
5
+H
2
SO
4
→SO
3
+4HPO
3
P
4
O
10
+H
2
N—C(O)—C(O)—NH
2
→NC—CN+4HPO
3
P
2
O
5
+CH
2
═C(CH
3
)—C(O)—OH+CH
3
OH→CH
2
═C(CH3)—C(O)OCH
3
+2HPO
3
P
2
O
5
reacts with ethyl ether to form triethyl phosphate:
P
2
O
5
+3(C
2
H
5
)
2
O→2(C
2
H
5
O)
3
P═O
The strong reactivity of phosphorus pentoxide makes the selection of the reaction solvent greatly restricted. The inventors of the present invention have tried using a solvent such as n-hexane, diethyl phosphate, and toluene, etc. for performing the reaction, in which the reaction of using n-hexane as a solvent is not ideal and has an extremely low yield. When diethyl phosphate is used as a solvent, the reaction has a very good yield. However, since the properties of diethyl phosphate are too close to the properties of the product bis-(pentaerythritol phosphate) phosphoric acid, they are difficult to be separated. Therefore, toluene is selected as a reaction solvent.
Pentaerythritol can be dissolved in diethyl phosphate solvent, therefore, after addition of P
2
O
5
, the reaction can take place at a reaction temperature of 90° C. While not dissolving in toluene, pentaerythritol will turn into a molten state when the temperature rises to 90° C. and can react with P
2
O
5
. Since pentaerythritol in its molten state has an extremely high viscosity and is difficult to agitate, the reaction yield is not high. Therefore, how to achieve an ideal agitation for pentaerythritol to have a sufficient contact with P
2
O
5
is a key factor in increasing the yield. Pentaerythritol does not dissolve at the boiling point of n-hexane at 68° C. and has no change in state at this temperature, this could be a reason why it does not react with P
2
O
5
in n-hexane.
2. Study on Reaction Temperature
Pentaerythritol does not react with P
2
O
5
in toluene solvent at a temperature lower than 70° C. under traditional stirring process. When the temperature increases to 90° C., pentaerythritol can undergo a phosphate esterification reaction. The reaction time is about 10 hours. When the temperature rises to 105° C., the reaction time can be reduced to 6 hours.
3. Effects of the Particle Size of Pentaerythritol
The reaction yield and purity can be increased when, prior to the reaction, pentaerythritol is ground in toluene in a ball mill.
4. Ball Mill Process
Based on the above studies 1~3, the key factors affecting the method of the present invention include: heating of the solvent, material with a fine particle size, and complete mixing in the reaction. Therefore, a ball mill is considered as a reactor to achieve a complete grinding, mixing and thermal insulation in the reaction. A suitable reaction time is 4-20 hours.
5. Formation of Phosphoric Acid in the Reaction
When 2 moles of pentaerythritol reacts with 1.5 mole of P
2
O
5
, 1 mole of bis-(pentaerythritol phosphate) phosphoric acid and 3.5 moles of water will be generated. Since 3 moles of water will react with 1 mole of P
2
O
5
to from 2 moles of phosphoric acid, and a consumption of P
2
O
5
occurs. Therefore, an excessive amount of P
2
O
5
should be used for all the pentaerythritol phosphate alcohol to be converted to bis-(pentaerythritol phosphate) phosphoric acid. A suitable mole ratio of pentaerythritol to P
2
O
5
is 4:3 to 1:2.
The reaction between melamine and bis-(pentaerythritol phosphate) phosphoric acid according to the present invention can be carried out in said ball mill or a conventional mechanical agitation reactor, preferably in a ball mill. The reaction can be carried out using acetonitrile or water as the solvent. According to the present invention, when the conventional mechanical mixing is used and acetonitrile is used as a solvent, the reaction can be completed
Ma Chong
Peng Yuen-Hsin
Wu Tseng-Rong
Chung-Shan Institute of Science & Technology
Ramsner Robert W.
Sackey Ebenezer
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