Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D211/00—Heterocyclic compounds containing hydrogenated pyridine rings, not condensed with other rings
  • C07D211/04—Heterocyclic compounds containing hydrogenated pyridine rings, not condensed with other rings with only hydrogen or carbon atoms directly attached to the ring nitrogen atom
  • C07D211/68—Heterocyclic compounds containing hydrogenated pyridine rings, not condensed with other rings with only hydrogen or carbon atoms directly attached to the ring nitrogen atom having one double bond between ring members or between a ring member and a non-ring member
  • C07D211/70—Heterocyclic compounds containing hydrogenated pyridine rings, not condensed with other rings with only hydrogen or carbon atoms directly attached to the ring nitrogen atom having one double bond between ring members or between a ring member and a non-ring member with only hydrogen atoms, hydrocarbon or substituted hydrocarbon radicals, directly attached to ring carbon atoms
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D211/00—Heterocyclic compounds containing hydrogenated pyridine rings, not condensed with other rings
  • C07D211/04—Heterocyclic compounds containing hydrogenated pyridine rings, not condensed with other rings with only hydrogen or carbon atoms directly attached to the ring nitrogen atom
  • C07D211/06—Heterocyclic compounds containing hydrogenated pyridine rings, not condensed with other rings with only hydrogen or carbon atoms directly attached to the ring nitrogen atom having no double bonds between ring members or between ring members and non-ring members
  • C07D211/36—Heterocyclic compounds containing hydrogenated pyridine rings, not condensed with other rings with only hydrogen or carbon atoms directly attached to the ring nitrogen atom having no double bonds between ring members or between ring members and non-ring members with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms
  • C07D211/40—Oxygen atoms
  • C07D211/44—Oxygen atoms attached in position 4
  • C07D211/46—Oxygen atoms attached in position 4 having a hydrogen atom as the second substituent in position 4
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D211/00—Heterocyclic compounds containing hydrogenated pyridine rings, not condensed with other rings
  • C07D211/92—Heterocyclic compounds containing hydrogenated pyridine rings, not condensed with other rings with a hetero atom directly attached to the ring nitrogen atom
  • C07D211/94—Oxygen atom, e.g. piperidine N-oxide

Definitions

• the present invention relates to a process for the preparation of 2,2,6,6-tetraalkylpiperidin-1- oxyls, such as 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO), via the corresponding 1 ,2,3,6- tetrahydro-2,2,6,6-tetraalkylpyridine, which latter is prepared by dehydration in the gas phase from 4-hydroxy-2,2,6,6-tetraalkylpiperidine on a metal oxide or semimetal oxide catalyst in the presence of water.
• TEMPO 2,2,6,6-tetraalkylpiperidin-1- oxyl
• Tetraalkylpiperidin-1-oxyl and, in particular, 2,2,6,6-tetramethylpiperidin-1-oxyl are products which have versatile uses and which may be used, for example, as polymerisation inhibitors during the distillation and purification of styrene or acrylates.
• EP-A-0 866 060 it is even possible to oxidise the olefinically unsaturated compound 1 ,2,3,6-tetrahydro-2,2,6,6-tetramethylpyridine to N-oxyl in the presence of alkaline earth salts or alkaline earth hydroxides without the double bond being attacked.
• suitable catalysts show a change of pH from 0.5 to 2 units after a certain time.
• the yield after an induction phase of about 1 week is said to be 70 or 82%.
• the dehydration is carried out in the presence of water on a metal or metal oxide catalyst, then the full catalytic effect is present from the start and there is no induction period.
• the acid strength is adjusted in situ by means of the water or water vapour present serving as modifier for the catalyst.
• the catalyst is continuously purified by the water or the water vapour so that standing times of several thousand hours result without the activity getting any worse.
• the reaction temperature can even be lowered to below 300° C.
• This invention provides a simple, efficient, low cost and at the same time ecologically compatible large-scale synthesis, for example for preparing the intermediate 1 ,2,3,6-tetrahydro- 2,2,6,6-tetramethylpyridine from 4-hydroxy-2,2,6,6-tetramethyipiperidine, and thus also a process for the preparation of TEMPO from readily accessible basic substances.
• the present process for the dehydration of 4-hydroxy-2,2,6,6-tetraalkyipiperidinepiperidine results in a high yield, can be carried out continuously or batchwise and yields the intermediate in high purity.
• this invention relates to the preparation of a compound of formula I (I), wherein
• R 1 f R 2 , R 3 and R 4 are each independently of one another C ⁇ -C 4 alkyl; R 5 is H or CH 3 ; and R 6 is H or C C 18 alkyl; from a compound of formula II
• Alkyl is, for example, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, dodecyl or octadecyl.
• the alkyl groups may be linear or branched.
• R r R is ethyl or propyl and the remaining R to R 4 are methyl.
• R 6 is preferably hydrogen or C C 4 alkyl, particularly preferably hydrogen.
• TTMP from 4-hydroxy-2,2,6,6-tetramethylpiperidine is that, which comprises dehydrating
• Suitable catalysts are Al 2 0 3 - or Si0 2 -gels, Si0 2 -AI 2 0 3 -cogels and also Si0 2 -ZrO 2 , SiO 2 -TiO 2 , Si0 2 -MgO-cogels, or mixtures thereof.
• Sheet silicates are also suitable, for example bento- nites, montmorillonites, sepiolite as well as natural and synthetic zeolites or also porous glasses.
• an aqueous solution of the educt may be in the range from 1 % by weight up to the saturation point at the corresponding temperature and pressure.
• the solutions can be prepared in the temperature range from room temperature up to about 100° C and can then be added to the reactor.
• an aqueous solution of the educt is advantageously carried out in an about 1 % to about 60 % by weight aqueous solution at the corresponding temperature, particularly advantageously in a 1-15 % by weight solution at room temperature and, very particularly advantageously, in a 5-14 % by weight solution at room temperature.
• the ratio of water vapour to the compounds of formula II during the addition of the educt is from 1 to 50 mol of water vapour / mol of educt, particularly preferably from 2 to 30 mol of water vapour / mol of educt, most preferably from 5 to 20 mol of water vapour / mol of educt.
• water vapour may have a temperature from 100° C to 600° C.
• the range from 200° C to 500° C is preferred and the range from 250° C to 400° C is particularly preferred.
• the addition to the reactor can be carried out by known methods. Suitable metering pumps and valves are commercially available.
• the temperature in the reactor is from 225 to 350° C, particularly preferably from 250 to 300° C and, very particularly preferably, from 260 to 290° C.
• the pressure in the reactor is usually from 500 to 10000 hectopascal, preferably from 1000 - 5000 hectopascal, particularly preferably from 1000 - 2000 hectopascal.
• a preferred embodiment of the process is that, which comprises carrying out the process continuously by spraying the melt into the reactor and adding water vapour.
• the catalyst can be placed in the reactor by known methods. In the batch operation it may, for example, be present in slurried form in the solvent, and in the continuous operation it may be fixed in the reactor and flowed through by the educt or water vapour.
• This invention also relates to a process for the preparation of compounds of formula III
• TEMPO 2,2,6,6-tetramethylpiperidin-1-oxyl
• the hydration of the compounds of formula (I), in particular of 1 ,2,3,6-tetrahydro-2,2,6,6- tetramethylpyridine (THTMP), is carried out by methods known per se.
• the hydration may be carried out, for example, continuously over a nickel catalyst in the gaseous phase.
• the product to be hydrated does not have to be purified beforehand and may also be added with residual water.
• Such continuous hydration processes are known to the skilled person and are described in "Katalytician Hydrtechniken im organisch-chemischen Laboratorium, F. Zymalkowski, 1965, Gustav Enke Verlag Stuttgart".
• Nickel skeleton catalysts usually being used (Ni on AI 2 O 3 - or e.g. SiO 2 substrates).
• the yield is normally very high and is usually from 96-98%.
• hydration processes are also known to the skilled person and are described, inter alia, in ⁇ ydrogenation Methods, Paul N. Rylander, 1985, Academic Press".
• Typical process parameters in the case of batchwise hydration are temperatures in the range from 30-100° C and a hydrogen pressure of about 50 bar, Pd- or Pt-catalysts usually being used which are normally bound to carrier materials.
• the ratio of educt to catalyst is usually from 50-1000 g/g.
• the oxidation step C) is known from the literature and has been described with different oxidants, for example tert-butylhydroperoxide or 3-chloroperbenzoic acid. Not least because of costs, H 2 O is particularly suitable as oxidant for use on an industrial scale, as is disclosed, inter alia, in EP-A-0 574 667.
• other catalysts are used without which the reaction times may take up to several days. Catalysts used are mainly transition metal compounds such as sodium tung- state, ammonium tungstate (e.g. GB 1 199 351 ) or phosphorus tungstic acid (Bull. Soc. Chim. Fr.
• Tungstates are mostly used in combination with the salt of ethylenediaminetetracetic acid (EDTA).
• EDTA ethylenediaminetetracetic acid
• a preferred process is that, in which the oxidation step is carried out in the presence of a dialkylamide.
• a dialkylamide such as di- methylformamide (DMF)
• DMF di- methylformamide
• TMP 2,2,6,6-tetramethylpiperidine
• Suitable dialkylamides are derived from C ⁇ -C 8 dialkylamides, preferably from C C 4 dialkyl- amides and particularly preferably from dimethylamides or diethylamides.
• the amides are preferably derived from C C 12 acids; C r C 6 acids are particularly preferred and the dialkylacetamides and dialkylformamides are very particularly preferred.
• dialkylamides are N,N-dimethylformamide (DMF) and N,N-dimethyl- acetamide. It is preferred to use 1-10 mol %, particularly preferably 2-5 mol %, of the dialkylamide.
• a particularly preferred process for the preparation of 2,2,6,6-tetramethylpiperidin-1-oxyl comprises hydrating in a first step
• This invention also relates to the use of dialkylamides when oxidising compounds of formula (la) to compounds of formula (III) with hydrogen peroxide.
• Another object of this invention is the use of a metal oxide or semimetal oxide catalyst for the catalytic dehydration of compounds of formula (II) in the presence of water or water vapour.
• Example A1 Dehydration of 4-hvdroxy-2,2,6,6-tetramethylpiperidine to 1.2.3.6-tetrahydro- 2,2,6,6-tetramethylpyridine on a laboratory scale
• a microreactor is charged with 5 ml of an AI 2 O 3 catalyst.
• a HPLC pump and a receiver with cold trap are connected to the microreactor.
• the reactor is heated in an oven to 275-300° C.
• a 13% by weight aqueous solution (deionised water) of 4-hydroxy- 2,2,6,6-tetramethylpiperidine is added continuously via the pump at 8 ml / hour.
• the two phases of the product solution are transferred to a 500 ml separating funnel and separated.
• the aqueous phase is shaken out twice with diethyl ether, the organic phases are combined and the highly volatile products and solvents are stripped off in a rotary evaporator. This yields crude 1 ,2,3,6-tetrahydro-2,2,6,6-tetramethylpyridine in 79% yield in the form of a yellow oil having a purity of 93%.
• Example A2 semipilot: 4-hydroxy-2.2,6,6-tetramethylpiperidine to 1 ,2,3,6-tetrahvdro-2.2.6.6- tetramethylpyridine
• the apparatus consists of a heatable cylindrical reaction vessel which is filled with 800 ml of AI 2 O 3 catalyst and heated to 270-280° C.
• a melt of 4- hydroxy-2,2,6,6-tetramethylpiperidine is added via a heatable feed inlet at 150-400 ml / hour.
• superheated water vapour of 280° C is added to the melt shortly before entry into the reaction tube.
• a condenser with a product receiver. Separation of the phases results in crude 1 ,2,3,6-tetrahydro-2,2,6,6- tetramethylpyridine in a 73-80% yield and having a content of > 85%.
• Example A3 Dehydration of 4__hvdroxy-2.6-diethyl-2,3,6-trimethylpiperidine to 1.2.3.6- tetrahydro-2,6-diethyl-2,3.6-trimethylpyridine on a laboratory scale
• a microreactor is charged with 5 ml of a AI 2 O 3 catalyst.
• a HPLC pump and a receiver with cold trap are connected to the microreactor.
• the reactor is heated in an oven to 275-300 °C.
• a 10% by weight aqueous solution (deionised water) of 4-hydroxy-2,6- diethyl-2,3,6-trimethylpiperidine is continuously added via the pump at 4 ml/h.
• the two phases of the product solution are transferred into a 250 ml separating funnel and separated. Further working up is carried out as described in Example A1.
• the 1 ,2,3,6-tetrahydro-2,6-diethyl-2,3,6-trimethylpyridine content of the organic phase is 83%.
• Example A4 Dehydration of 4-hvdro ⁇ y-1.2.2.6,6-pentamethylpiperidine to 1 ,2,3,6-tetrahvdro- 1.2.2,6,6-pentamethylpyridine on a laboratory scale
• a microreactor is charged with 5 ml of a Al 2 0 3 catalyst.
• a HPLC pump and a receiver with cold trap are connected to the microreactor.
• the reactor is heated in an oven to 260-280 °C.
• a 4% by weight aqueous solution (deionised water) of 4-hydroxy- 1 , 2,2,6, 6-pentamethylpiperidine is continuously added via the pump at 6 ml/h.
• the two phases of the product solution are transferred to a 250 ml separating funnel and separated. Further working up is carried out as described in Example A1.
• the 1 ,2,3,6-tetrahydro-1 ,2,2,6,6-pentamethylpyridine content of the organic phase is about 37 %.
• Example A5 Dehydration of 4-hvdroxy-1.2.2.6.6-pentamethylpiperidine (HPMP) to 1 ,2.3.6- tetrahvdro-1 ,2,2,6,6-pentamethylpyridine on a laboratory scale
• a microreactor is charged with 5 ml of a Al 2 0 3 catalyst.
• a HPLC pump, a heatable feed inlet and metering device and a receiver with cold trap are connected to the microreactor.
• the reactor is heated in an oven to 260-280°C. At this temperature, 8 ml of deionised water and 0.5 g of a 4-hydroxy-1 ,2,2,6,6-pentamethylpiperidine melt per hour are added continuously.
• the two phases of the product solution are transferred to a 250 ml separating funnel and separated. Further working up is carried out as described in Example A1.
• the 1 ,2,3,6-tetrahydro-1 ,2,2,6,6-pentamethylpyridine content of the organic phase is about 48 %.
• a microreactor is charged with 5 ml of a Ni/NiO-AI 2 0 3 catalyst.
• a HPLC pump and a receiver with cold trap are connected to the microreactor.
• the reactor is heated in an oven to 250° C in a N 2 stream (50ml/minute). When that temperature is reached, increasing amounts of hydrogen are admixed to the N 2 stream until the proportion of hydrogen is 100%. Subsequently, the temperature is elevated for 30 minutes to 350° C and then lowered to 100° C. At this temperature, the THTMP of Example A1 is added in an amount of 4.2 ml/h via the pump. At the same time hydrogen is added at a rate of 50 ml/minute. The reaction is completed quantitatively at 110-130° C.
• Example B2 Hydration of 1.2,3.6-tetrahvdro-2,6-diethyl-2,3.6-trimethylpyridine to 2.6-diethyl- 2.3,6-trimethylpiperidine (DETMP) on a laboratory scale
• a microreactor is charged with 5 ml of a Ni/NiO- AI 2 O 3 catalyst.
• a HPLC pump and a receiver with cold trap are connected to the microreactor.
• the reactor is heated in an oven to 250 °C in a N 2 stream (50 ml/min). When that temperature is reached, increasing amounts of hydrogen are admixed to the N 2 stream until the proportion of hydrogen is 100%. Subsequently, the temperature is elevated for 30 minutes to 350°C and then lowered to 100°C.
• the 1 ,2,3,6-tetrahydro-2,6-diethyl-2,3,6-trimethylpyridine of Example A3 is then added in an amount of 4 ml/h via the HPLC pump.
• hydrogen is added at a rate of 50 ml/min.
• the reactor temperature rises to 120 - 130 °C. The reaction is almost quantitative and the entire DETMP yield is virtually 100%.
• Example B3 Hydration of 1.2,3,6-tetrahvdro-1.2.2,6.6-pentamethylpyridine to 1 ,2.2.6.6- pentamethylpyridine (PMP) on a laboratory scale
• a microreactor is charged with 5 ml of a Ni/NiO- AI 2 O 3 catalyst.
• a HPLC pump and a receiver with cold trap are connected to the microreactor.
• the reactor is heated in an oven and in a N 2 stream (50 ml/min) to 250 °C. When that temperature is reached, increasing amounts of hydrogen are admixed to the N 2 stream until the proportion of hydrogen is 100%. Subsequently, the temperature is elevated for 30 minutes to 350°C and then lowered to 100°C.
• the 1 ,2,3,6-tetrahydro-1 ,2,2,6,6-pentamethylpyridine (organic phase of Examples A4/A5) is then added in an amount of 4 ml/h via the HPLC pump. At the same time hydrogen is added at a rate of 50 ml/min.
• the reactor temperature rises to 110 - 120 °C.
• the reaction is almost quantitative and the entire PMP yield is practically 100%.
• TMP 2,2,6,6-tetramethylpiperidine
• N,N,-dimethylformamide (0.11 mol).
• the mixture is heated, with stirring, to 70-80°C and then 263.6 g (2.3 mol) of 35% hydrogen peroxide are added dropwise over 4 hours such that the temperature of the reaction mixture does not ex- ceed 85°C.
• the pH of the reaction mixture falls in the course of the addition from about 8.3 to about 6.2 and the reaction mixture turns an intense dark red.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Hydrogenated Pyridines (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Nitrogen Condensed Heterocyclic Rings (AREA)

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• 2000
  • 2000-01-31 SK SK1112-2001A patent/SK11122001A3/sk unknown
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  • 2000-01-31 WO PCT/EP2000/000733 patent/WO2000046202A2/en not_active Application Discontinuation
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  • 2000-01-31 CN CN00803344A patent/CN1352633A/zh active Pending
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