Organic compounds -- part of the class 532-570 series – Organic compounds – Four or more ring nitrogens in the bicyclo ring system
Reexamination Certificate
2000-09-21
2002-02-19
Ford, John M. (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Four or more ring nitrogens in the bicyclo ring system
Reexamination Certificate
active
06348592
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for the production of organic solvent soluble squaraine dyes. More particularly, this invention relates to an improved method of using a series of reactions and reaction mixtures to provide dihydroperimidine squaraine dyes.
BACKGROUND OF THE INVENTION
Squaraine dyes are known to possess photoconductive and semi-conductive properties. These features have made then very attractive for various industrial applications such as in electrophotographic photoreceptors, organic solar cells, plasma display panels, and optical recording media, and as photopolymerization sensitizers, infrared radiation absorbing inks or paints, and acutance or antihalation dyes in photosensitive media including photothermo-graphic materials.
An early synthetic method for preparing dihydroperimidine squaraine dyes is described by Bello et al.,
J. Chem. Soc., Chem. Commun
., 1993, pp. 452-454. This method is used in EP-A-0 748,465B 1 [counterpart to WO95/23357 and U.S. Pat. No. 5,380,635 (Gomez, et al.)] for providing a squaraine dye having hexanoic acid ester substituents on the outer dihydroperimidine rings. In this method, 1,8-diaminonaphthalene and 1,3-dihydroxyacetone dimer are first reacted to form 2,2-bis(hydroxymethyl)-2,3-dihydroperimidine (the first intermediate). In the second step, the 2,2-bis(hydroxymethyl)-2,3-dihydroperimidine is reacted with squaric acid to form a bis[2,2-bis(dihydroxymethyl) dihydroperimidine] squaraine dye (the second intermediate, a tetrahydroxy squaraine compound). Finally, this tetrahydroxy squaraine intermediate is reacted with hexanoyl chloride to form the dye. U.S. Pat. No. 5,625,062 (Mader et al.) describes a number of other known synthetic methods for preparing squaraine dyes. Each of these known methods is said to suffer from various problems involving reactants, unwanted by-products, low yields, and product instability. Those problems were addressed by the synthesis described in Columns 4 and 5 therein. The synthesis described is similar to that of U.S. Pat. No. 5,380,635 (noted above). The reaction solvents and conditions were changed to improve yields.
One important feature of both U.S. Pat. No. 5,380,635 and U.S. Pat. No. 5,625,062 is the use of the expensive reagent squaric acid in the second reaction step.
U.S. Pat. No. 5,959,105 (Harada et al.) describes another method for preparing squaraine dyes having hexanoic acid ester substituents on the dihydroperimidine rings. Dipentylcarbonyloxymethyl ketone is reacted with 1,8-diaminonaphthalene to form 2,2-dipentylcarbonyloxylmethyl-2,3-dihydroperimidine. Reaction of this diester with squaric acid in a solvent mixture of butanol/toluene forms the squaraine dye having hexanoic acid ester substituents on the dihydroperimidine rings. Purification was said to be achieved by column chromatography on silica gel and elution with chloroform.
Problem To Be Solved
The synthetic methods described above have a number of disadvantages.
In both EP-A-0 748,465B 1 and U.S. Pat. No. 5,625,062 the first reaction step, preparation of 2,2-bis(hydroxymethyl)-2,3-dihydroperimidine intermediate, is carried out in an alcoholic solvent, with or without added acid catalyst. While this procedure can yield good quality product, the alcohol solvent should be completely removed before using the 2,2-bis(hydroxymethyl)-2,3-dihydroperimidine in the subsequent step. A method for preparing this intermediate while avoiding this problem would be desirable.
The second reaction in this synthesis also presents several difficulties. While the second intermediate (tetrahydroxy squaraine) can be obtained in high nominal yield, it is not obtainable in high purity (63-87% described in U.S. Pat. No. 5,625,062). No teaching is provided to purify this intermediate, and its low solubility in most solvents precludes its ready purification by such conventional methods as recrystallization or chromatography. Thus, the impurities must be carried over into the third reaction step, potentially introducing contaminants into the final reaction step.
Moreover, the second reaction step is carried out in either n-propanol (EP-A-0 748,465B1) or a mixtures of solvents including octanol or heptanol (U.S. Pat. No. 5,625,062). The use of n-propanol is undesirable because the second intermediate is difficult to separate from it. The use of mixtures of longer chain alcohols is also undesirable because of their high cost when compared with that of shorter-chain alcohols.
The thermal instability of the second intermediate is also a serious concern from a safety point of view, especially for its large-scale production. To avoid this problem, U.S. Pat. No. 5,625,062 teaches washing the second intermediate with ethanol followed by ethyl acetate. The still-damp second intermediate is then used in the subsequent step. This also introduces several practical and costly problems for large-scale production operations by exposing operators to flammable and toxic solvents or by requiring expensive safety measures.
In the third step of the synthetic method, formation of the squaraine dye, additional difficulties arise. In EP-A-0 784,465B1, the esterification is preformed in the presence of 4-dimethylaminopyridine, an expensive and toxic reagent. In U.S. Pat. No. 5,625,062 the esterification is performed in the presence of pyridine, which while less expensive, is also toxic. Additionally, because of the low solubility of the tetrahydroxy squaraine (second intermediate) in the reaction mixture, it is usually present in the final isolated reaction product (up to 11% is noted in U.S. Pat. No. 5,625,062). This impurity diminishes the usefulness of the desired squaraine dye. The amount of insoluble intermediate remaining varies from batch to batch and requires either an additional filtration step for its removal or results in clogging of coating equipment and poor coatings containing particulates and/or exhibiting streaks.
Still another disadvantage to the synthetic methods noted above relates to the use of squaric acid in the second reaction step. Squaric acid is the most expensive raw material used in preparing squaraine dyes. Due to poor yields in these methods, and the use of squaric acid early in the synthesis, more squaric acid is required to obtain a given quantity of squaraine dye.
Although the synthesis described in U.S. Pat. No. 5,959,105 appears to have only two reaction steps, the dipentylcarbonyloxymethyl ketone also requires preparation. U.S. Pat. No. 5,959,105 provides no teaching as to synthetic methods of its preparation, its yield, or its purity. Moreover, the purification of the final product requires use of the highly toxic solvent chloroform. Using this method for large-scale production would be costly and potentially harmful to the environment.
There is clearly a need for a more efficient method to produce dihydroperimidine squaraine dyes that avoids the difficulties and disadvantages of the known methods described above and that can be readily used in a cost effective manner in large-scale production.
SUMMARY OF THE INVENTION
The present invention provides a solution to the problems noted above with a method of making a compound comprising:
A) reacting the following Compound I with the following Compound II to form the following Compound III in a first reaction mixture comprising one or more organic solvents, wherein the molar ratio of Compound I to Compound II initially in the first reaction mixture is from about 1.5:1 to about 2:1,
B) reacting the resulting Compound III with an organic acylating agent to form the following Compound IV in the presence of one or more organic solvents, wherein the initial molar ratio of Compound III to the organic acylating agent is from about 0.4:1 to about 0.6:1,
wherein R in Compounds IV and V below is a monovalent organic radical derived from the organic acylating agent,
and
C) reacting the resulting Compound IV with squaric acid to form the following Compound V in a separate reaction mixture under conditions that provide for at least partial remo
Bernard Lori S.
Ramsden William D.
Valente Louis F.
Eastman Kodak Company
Ford John M.
Tucker J. Lanny
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