DE1695229C3 - Process for the substitution of chlorine atoms by fluorine atoms in difluorotnchlor or tnfluor dichloropynes - Google Patents

Description

The invention relates to a method Substitution of chlorine atoms by fluorine atoms in difluoro-trichloro- or tritUiiir-dichloropyridine or their mixtures.

It is known that fluorochloropyridines thereby can be prepared by using chloropyridines with anhydrous potassium fluoride in a polar aprotic solvent. preferably tetramethylene sulfone, heated. For example, 2-chloropyridine gives 2-fluoropyridine; 2.3-dichloropyridine gives 3-chloro-2-fluoropyridine: 2.3.5-Trichlorpyridii ·. results 3.5-dichloro-2-fluoropyridine; a mixture of isomers Trachloropyridine gives moderate yields of an approximately equimolar mixture of 3,5-dichloro-2,6-difliiorpyridine and 3-chloro-2.4.6-fluoropyridine: and pentachloropyridine gives 3.5-dichloro-2.4,6-tritluoropyridine and a small amount of 3-chloro-tetrafluoropyridine. It is also known. Pentafluoropyridine. 3-chloro-tetrafluoropyridine and 3,5-dichloro-trifluoropyridine thereby hcr / stellen that one pentachloropyridine with anhydrous potassium fluoride in the absence of a Solvent heated to temperatures from Ί00 to 48 «C under autogenous pressure. With all these reactioners however, the response times are very long. The shortest known reaction times are 17 hours and the longest 20 days.

It has now been found that the reaction can also take place in the order of 1 second if you use a certain way of working.

So according to the invention is a method for Substitution of chlorine atoms by fluorine atoms in difluoro-trichloro- or trifluor-dichloropyridines or Proposed mixtures thereof, which is characterized in that the with an inert carrier gas dilute gaseous starting compounds at a temperature of 750 to 770 "C by a eutectic Conducts a melt of potassium fluoride and potassium chloride, the contact time being about 1 second.

In principle one could assume that the method z. B. is also applicable to pentachloropyridine, but at the preferred temperature of the melt, namely above 700 ° C, a certain decomposition of the pentachloropyridine occurs. According to the invention The fluorinated chloropyridines used are more stable to heat. So now there is a suitable way to the tetrafluorochloropyridines and to pentafluoropyridine in that one first has a difluorotrichloropyridine or trifluoro-dichloropyridine from pentachloropyridine, for example by heating it in tetramethylene> ulfon with anhydrous potassium fluoride and that one then ditluorotrichloropxridine or the trilluoro-dichloropyridine or a mixture thereof in the process according to the invention subject.

The eutectic mixture used according to the invention from 'E KCI contains 45 .Violprozent KF and 55 mole percent KCI and melts at approximately 605 C.

A suitable way / for carrying out the method according to the invention consists in this. tk> s starting material in a stream of an inert carrier gas. /. ti. dry nitrogen, which is reserved at about 300 C / t. through a platinum tube at the bottom of a melt which has a depth of about 60 cm and is located in an electrically heated, graphite-lined stainless steel container. The container is made gas-tight except for the inlet and outlet pipes, and the outlet pipe is connected to suitable cold traps in which the reaction products from the gas stream are condensed. The products are then separated by fractional distillation.

The invention is illustrated by the following examples. The carrier gas passed in all tests from dry nitrogen: and the device used was the one just described, which had a melt depth of 56 cm.

All percentages are expressed by weight.

example 1

The starting halopyridine was trifluorochloropyridine. and the temperature of the melt was 750 C. The flow rate was 150 ml min. nitrogen and 95 g hr. C ₃ NF ₃ Cl; the reaction time was I ¹ 'hours. The contact time between the melt and the C ₅ NT ₃ CI ₂ was determined to be approximately 1 second. The products collected in the traps amounted to 115 g, which corresponds to a yield of approximately 81 ° ₀ . The products are composed as follows:

C ₅ NF ₅ 17.0%

C ₅ NF ₄ Cl 22.8 ° _O

C ₅ NF ₃ CU 58.5%

C ₅ NF ₂ Cl ₃ 1.7 °. "

Example 2

The reaction conditions of Example 1 were used again, with the exception that the flow rate of the C ₅ NF ₃ CI _{2 was} 47 g / hour, the duration was 2 hours and the melting temperature was 77O ^C. The collected products made of 70 g, corresponding to a yield of 75 ° / _0th The products are composed as follows:

C ₅ NF ₅ 6.8%

C ₅ NF ₄ CI 26.2 ", Ό

C ₅ NF ₃ Cl ₂ 57.0 ° / ₀

CjNFXI, 10.0 ¹ V ₀

Example 3

The reaction conditions of Example I were used again, with the difference that the flow rate of the C ₅ NF ₃ Ci _{2 was} 40 g / hour, the duration was 2 hours and the melting temperature was 770.degree. The collected products were 59 g. corresponding to a yield of 74%. The products are composed as follows:

C ₅ NF ₅ 9.7%

C ₅ NF ₁ CI 27.6%

C ₅ NR ₁ Cl 59.0 »/ ₀

C ₅ NF ₂ CI ₃ 3.7%

Example 4

In this; In the example, a mixture was used as starting material which contained 58 mol percent C ₅ NF ₂ Cl ₃ and 42 mol percent C ₅ NF ₃ Cl ₂ . This mixture was at a flow rate of 47 g / h. in a nitrogen carrier gas of 150 ml / min, passed through the melt. The temperature of the Schmcl / e was 770 C i> and the reaction time 2 hours. The collected products were 82 g, corresponding to a yield of 87%. The products are composed as follows:

C ₅ NF, 10.0%

C-, NF ₁ Cl 24.0%

^D C ₅ NF ₁ CU 57.2%

C ₅ NF ₂ CI ₃ 8.8%,

Example 5

ίο As in Example 4, a starting material was used which consisted of a mixture of halopyridines, namely 65 mol percent C ₅ NF ₃ Cl ₂ and 35 mol percent C ₅ NF ₂ Cl ₃ . The flow rate of the same was 40 g hour and that of the nitrogen 150 ml min. The temperature of the melt was 77O ^: C and the reaction time was 2 hours. The collected products were 52 g. corresponding to a yield of 65%. The products are composed as follows:
20th

C ₅ NF ₅ 17.2%

C ₅ NF ₁ Cl 29.0%

C ₅ NF ₃ Cl, 50.2%

C ₅ NF ₂ C, 3.6%

Claims (1)

Claim: Procedure / ur substitution of Ciiloralorncn by eluor atoms in dilluor-trichloro- h / .vv. Trilluor dichloropridines or mixtures of these, since I u r c h e k e η η / e i c h η e t. that one gaseous diluted with an inert carrier gas Starting compounds in a teniperalur from 750 to 770 C by a eutectic mixture of potassium chloride and potassium chloride conducts, the contact / time being about 1 second.