Organic compounds -- part of the class 532-570 series – Organic compounds – Four or more ring nitrogens in the bicyclo ring system
Reexamination Certificate
2001-03-08
2003-05-27
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
C544S218000
Reexamination Certificate
active
06570011
ABSTRACT:
This invention relates to a process for the preparation of a stabilized aqueous alkali metal-2-hydroxy-4,6-dichloro-s-triazine (AHDT) solution and use thereof.
The alkali metal and alkaline earth metal salts of 2-hydroxy-4,6-dichloro-s-triazine, especially the sodium salt thereof (NHDT), are preferred hardening agents for gelatinous materials which are used in particular for photographic purposes. Accordingly, there are numerous known methods of preparing these triazine derivatives, and also of hardening solutions containing them.
However, the stability of the hardening solutions remains problematic. This is because both during synthesis and storage of the carbonate-containing hardening solutions, and often during their use, carbon dioxide is formed and the triazines are hydrolyzed to the corresponding monochlorinated compounds. Another particular disadvantage connected with the formation of carbon dioxide is that the gas generates bubbles in the photographic layers produced with the hardening agent.
To overcome these difficulties, it has been suggested in the past that the aqueous hardening solutions be buffered with a water-soluble borate (DE-OS 28 20 108). According to the DE-OS 29 10 726, the buffering effect can be enhanced by means of an alkali metal hydroxide and possibly by addition of water-soluble organic solvents, for example acetone, which are inert under the reaction conditions. The amount of alkali borate used in this case is only 0.02 to 2 moles per mole AHDT.
It has been found in practice, however, that neither the sole measure of buffering with borates nor the additional use of alkali metal hydroxides solves the problem of carbon dioxide formation. A further disadvantage of the known synthesis method is the very slow formation of the respective alkali metal-2-hydroxy-4,6-dichloro-s-triazine (AHDT).
The object of this invention was thus to provide a process for the preparation of a stabilized aqueous alkali metal-2-hydroxy-4,6-dichloro-s-triazine (AHDT) with which, in particular, undesirable formation of CO
2
is suppressed both during the synthesis reaction and during storage and use of the prepared AHDT solution. In addition, the preparation process should be easy and quick to carry out.
This object was established by
(a) providing an aqueous alkali hydrogencarbonate and/or acetone starting solution,
(b) adding cyanuric chloride and an alkali lye under such conditions that the temperature does not rise above 25° C. and the pH does not drop below 5.5;
(c) adding an alkali salt of an organic acid for the case that in (a) a hydrogencarbonate-containing solution was used, or adding an alkali hydrogen carbonate for the case that in (a) exclusively acetone was used;
(d) adding a stabilizer selected from an alkali borate and/or an alkali (hydrogen) phosphate and/or an alkali hexacyanoferrate (II), and
(e) if necessary adjusting the pH to the desired value with acid.
In a preferred embodiment, the process is conducted at temperatures between 5 and 40° C. in the following way:
(a) providing an aqueous 0.1 to 1.0 wt. % alkali hydrogencarbonate solution and/or a 0.5 to 5 wt. % acetone solution as starting solution, followed by
(b) adding 8 to 16 wt. % cyanuric chloride, expressed in terms of the solution from (a); wherein during the addition of cyanuric chloride, 1 equivalent expressed in terms of cyanuric chloride of a 25 to 50 wt. % alkali lye, is added at a temperature not exceeding 25° C. to the suspension in such a manner that the pH of the reaction mixture does not drop below 5.5;
(c) subsequently adding, during a stirring period of 2 to 30 hours, 0.1 to 1.5 wt. ‰ of an alkali lauryl sulfate for the case that in (a) a hydrogen-carbonate-containing solution was used, or of 0.5 to 1.0 wt. % of alkali hydrogen carbonate for the case that in a) exclusively acetone was used, both weight precentages being expressed in terms of the overall solution;
(d) finally, adding 0.3 to 1.2 wt. %—expressed in terms of the overall solution—of an alkali borate and/or of dialkali hydrogenphosphate and/or of potassium hexacyanoferrate (II), and
(e) if necessary, adjusting the pH to a value in the range from 8 to 9.5 with an acid.
Surprisingly, it was found that very small amounts of acetone or even the complete absence of acetone have no deleterious effect at all on the course of the reaction or on the reaction time. In view of the known prejudice—contained, for example, in the DE-OS 29 10 726—this was in no way to be expected. Moreover, particularly the use of alkali hydrogen carbonate permits wide variation in the way the process is conducted, it being possible at any time to quantitatively buffer the theoretically forming carbon dioxide.
Due to the use of alkali hydrogen carbonate, the process according to the invention indeed permits a wider temperature range, for example from 5 to 40° C., although temperatures between 10 and 20° C. are preferred. However, these relatively low temperatures have no deleterious effect whatsoever on the speed of reaction of the overall process.
For the process described here, sodium and potassium are preferred as alkali metals and have proved highly suitable. Using the same alkali metal for all steps of the process has the advantage that one obtains the pure sodium- or pure potassium-2-hydroxy-4,6-dichloro-s-triazine; however, it is also possible to use mixtures of these products.
The respective alkali hydrogencarbonate can be provided as aqueous starting solution, in which case a 0.5 to 0.8 wt. % solution is preferred. Alternatively, it can be added later on in the process, namely in step (c), if in step (a) aqueous acetone solution was used exclusively—according to the invention preferably in an amount of 1.0 to 2.0 wt. %. It is also possible, however, to start with a mixture consisting of alkali hydrogencarbonate and acetone in arbitrary proportions, provided amounts are within the range claimed.
The choice of alkali lye for step (b) will depend on which alkali hydrogencarbonate is used: if NaHCO
3
is used in step a) and/or step (d), it is preferable to add NaOH, whereas if KHCO
3
is used, it is preferable to add potassium lye in step (b).
All in all, there are thus no strict parameters governing the way in which the process of the invention is conducted. To optimize the course of the reaction, however, it is recommended that the amount of cyanuric chloride used in step (b) preferably be in the range from 10 to 12 wt. % expressed in terms of the solution from (a). The reaction sequence is likewise speeded up by selecting a preferred stirring time of 3 to 6 hours in step (c).
Like the alkali lye in step (b), the alkali salt added in step (c)—preferably the alkali salt of a C
10
-C
20
organosulfuric acid, in particular alkali lauryl sulfate—can be selected specifically to match the respective alkali hydrogencarbonate and thus to ensure a pure product.
As already explained, the principal objective of developing the process claimed here was to suppress the undesirable formation of CO
2
. This objective is achieved among other things by the addition of stabilizing and buffering substances in step (d) of the process according to the invention, preference being given to the alkali borates Na
2
B
4
O
7
or K
2
B
4
O
7
, their respective pentahydrates or decahydrates or mixtures thereof; as representatives of the alkali (hydrogen)phosphates, which are likewise suitable according to the invention, trialkali phosphates, alkali hydrogenphosphates and, in particular, dialkali hydrogenphosphates such as disodium and dipotassium hydrogenphosphate are preferred; the choice may again depend on the alkali hydrogencarbonate selected in each case.
For the most part, the pH does not constitute a limiting parameter for the process claimed. However, to ensure complete hydrolysis of the cyanuric chloride, it may be necessary according to the invention to adjust the pH at the end of step (d) to a value between 8.0 and 9.5 using an acid; wherein a mineral acid is recommended, preferably hydrochloric acid. It is especially beneficial if the pH is in the range from
Balasubrasubramanian Venkataraman
Degussa - AG
Ford John M.
Fulbright & Jaworski L.L.P.
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