T 0198/84 (Thiochloroformates) 28-02-1985

1. The appeal complies with Articles 106 to 108 and Rule 64 EPC and is therefore admissible.

2. According to the title, the subject-matter of the patent concerns a process for the preparation of thiochloroformates. According to the preamble to the description in the contested patent specification, these compounds are usually prepared by reacting mercaptans with phosgene in the presence of a catalyst. The citation (1) describes a process of this kind in which catalytic amounts of a carboxylic acid amide are used. Although this process permits yields of up to 90% of the theoretical maximum, it is not possible to reprocess the reaction deposits by distillation without previously removing the catalyst, because of decomposition, discoloration of the distillate or sublimation of solids. The catalyst is removed by washing with water or aqueous hydrochloric acid, causing a degree of hydrolysis of the thiochloroformates and thereby adversely affecting the yield and quality of the desired end product. Moreover removing the catalyst by washing with water or aqueous hydrochloric acid makes the process more expensive, particularly on a commercial scale (cf. page 2, lines 19 to 32).

3. Given the state of the art, therefore, the technical problem was to improve the yield of the process for the preparation of thiochloroformates by phosgenating mercaptans and at the same time to simplify the reprocessing of the reaction mixture. In order to solve this problem, the patent specification proposes that the carboxylic acid amide or a urea derivative be used in an amount of from 0.02 to 0.2 mol% relative to the mercaptan. Experimental evidence shows that the problem is indeed solved: the only experiments which are comparable, having been carried out with amide catalysts, consistently produced higher yields without washing with water (cf. Examples 2, 3 and 5 to 7 together with the comparison), the improvement amounting to at least 11.6% (see Example 3 together with the comparative example) and at most 35.7% (Example 6 together with the comparison). These figures also indicate that the improvement in yield goes markedly beyond the mere range of fluctuation which would normally be expected for such values. The results shown in the penultimate lines relating to the comparative experiments set out in the table had to be disregarded because they were not carried out in accordance with the teaching in (1), i.e. with removal of the catalyst by washing the reaction mixture with water and subsequent distillation. It is not possible to accept the appellant's objection that one of the comparative experiments is relevant because the wrong method of analysis was used, namely gas chromatography. He neither offers evidence for his assertion nor explains why any error which might occur when the same methods are used in both series of experiments (example and comparative experiment) is not eliminated, even if the result is slightly disorted by the substantial heating of the samples to be analysed.

4. The appellant stated in the course of the oral proceedings that he was unable to recognise the novelty of the process according to the contested patent; however, further discussion of this matter was unnecessary as it would have to take account of what was essentially normal practice in all patent offices, namely to regard only what had been described explicitly in prior-art documents as prejudicial to novelty. This statement prompts the Board to point out once again that this view disregards the purpose of Article 54(1) EPC, which is to prevent the state of the art from being patented again, as already laid down in Decision T 12/81 "Diastereomers/BAYER" (OJ of the EPO 8/1982, 296, 301). Since novelty is an absolute concept, a definition of an invention which differs only in its wording is insufficient; what has to be established in the examination as to novelty is whether the state of the art is likely to reveal the content of the invention's subject-matter to the skilled person in a technical teaching.

5. If this criterion is applied in the present case, it is found that the process according to (1) does not differ from the process according to the patent in question with regard to the starting materials and end products. There is also agreement in respect of the carboxylic acid amide catalyst, even if the latter is more broadly defined in the contested patent than in (1). The sole difference between the two processes consists in the use of different amounts of catalyst. According to (1), "catalytic amounts" are to be used (cf. Claim 1). Even in the absence of a separate definition in (1), the skilled person understands this - as the appellant concedes - to mean the range of substoichiometric amounts relative to one of the reactants. This range extends to a lower limit which in theory can be referred to as greater than zero. Mathematically, therefore, the range of the catalytic amount reaches from >0 to <100 mol% relative to 1 mole of a reactant. Such an extensive numerical range does not necessarily represent a disclosure, ruling out a selection from it, of all the numerical values between these minimum and maximum values if, as in this case, the sub-range selected is narrow and sufficiently far removed from the known range illustrated by means of examples. The claimed range of 0.02 to 0.2 mol% relative to the mercaptan, which has been specifically singled out, does indeed represent only a small specimen from the known range extending from >0 to <100 mol%. Moreover the essential portion of the known teaching according to (1) (cf. the 22 examples) specifies the use of catalyst concentrations of between 2 and 13 mol% relative to the mercaptan, a range removed by at least a power of ten from the selected range claimed. The subrange singled out here in the claim thus represents a quantitative range which has not yet been individualised and whose application in the production of thiochloroformates by the process according to the contested patent is new.

6. The same novelty test is also applied with the same result to chemical substances belonging to a prior-art group of substances, which has been defined in a formula, without being individualised. Thus, in Decision T 181/82 "Spiro compounds" (OJ of the EPO 9/1984, 401, 410, 411), the Board did not dispute the novelty of the whole of a group of substances specified by the reaction of a single aminospirane with a C1-C4-alkyl bromide. In fact, of the nine reaction products theoretically covered by this definition only the methylation product was regarded as individualised and therefore as belonging to the prior art. (C4-alkyl does not denote a single substance, but the group of all butyl derivatives.) The Board is aware that, for structural reasons, the numerical definition of a group of chemical substances can relate only to whole numbers, whereas the range of numbers under consideration in the present case additionally incorporates any values between the whole numbers. These special features of the two specified ranges, which are defined by minimum and maximum values, do not justify a different application of the concept of selection in the examination as to novelty. This is particularly so in the present case because the selection in question is numerically narrower than that in the cited Decision "Spiro compounds".

7. It remains to be established whether this view of novelty really entails more than just a formal delimitation of the process concerned vis-à-vis the state of the art. It would be delimited only in respect of the wording of the definition of the invention, but not in respect of its content, if the selection were arbitrary, i.e. if the selected range only had the same properties and capabilities as the whole range, so that what had been selected was only an arbitrary specimen from the prior art. This is not the case, since the effect of the substantial improvement in yield may be believed to occur only within the selected range, but not over the whole known range ("purposive selection"). To prevent misunderstanding, it should be expressly emphasised that when examining so-called selection inventions as to novelty the Board adheres to the principle that the sub-range singled out of a larger range is new not by virtue of a newly discovered effect occurring within it, but must be new per se (cf. T 12/81 "Diastereomers/BAYER", OJ of the EPO 8/1982, 296, 303). An effect of this kind is not therefore a prerequisite for novelty; in view of the technical disparity, however, it permits the inference that what is involved is not an arbitrarily chosen specimen from the prior art, i.e. not a mere embodiment of the prior description, but another invention (purposive selection).

8. It therefore has to be established whether the process according to the patent under consideration involves an inventive step. As already stated, the only citation in connection with the process describes the phosgenation of mercaptans into thiochloroformates in the presence of catalytic amounts of a carboxylic acid amide whose structure is designated in greater detail. According to the examples the concentration of catalyst lies between 2 and 13 mol%, yields of between 44 and 90% being achieved according to the type of catalyst and the reprocessing technique. For example, the minimum and maximum yield values are 61 and 84% with 2% of catalyst, 76 and 88% with 3%, 72 and 88% with 4%, 80 and 82% with 5%, and 79 and 90% with 6%. These values cannot be compared with one another because the structure of the catalyst was varied in all the examples. But the yields indicated in each example and the high yield obtained in certain cases indicate that the achievement of good yields is an important aspect of the process according to (i). In view of this, the statement in (i) that catalytic amounts of an amide catalyst are to be used can be distilled into the specific teaching that the amount of catalyst to be used to to achieve good yields is from 2 mol% upwards. According to the proprietor of the patent, it is a matter of common knowledge that larger amounts of catalyst normally produce higher yields. This coincides with the view of the appellant, who himself conceded during the oral proceedings that it was common knowledge among skilled persons that in the case of dissolved catalysts such as amide catalysts a reduction in the concentration of catalyst slows the reaction down. Given the problem of improving the yield by comparison with (i), therefore, the skilled person would have tended to increase the concentration of catalyst rather than reduce it if he had contemplated solving the problem through the quantities used to influence the yield. The proposal by the patent proprietor, whereby the amount of catalyst is to be purposively reduced in spite of the conventional teaching, was therefore not obvious to the skilled person.

9. When the appellant further asserts that a reduction in the amount of catalyst was an obvious solution if only in order to simplify the reprocessing operation, he disregards the dual nature of the problem, which consists in increasing the yield while at the same time simplifying the process. Confronted with this dual problem, the skilled person would not consider a proposed solution if it had to be assumed that, while solving one of the problems, it prevented a solution to the other. The present case involves a seemingly insuperable conflict between solutions, since a reduction in the concentration of catalyst, which was economically acceptable, was ruled out ab initio because it had no prospect of bringing about the desired improvement in yield at the same time.

10. To summarise, the teaching according to Claim 1 of the contested patent is new and involves an inventive step. The sub-claims dependent on this claim relate to special embodiments of the process according to the main claim, whose patentability applies to them as well.