CN107915673B

CN107915673B - Synthesis method of 2,2,6, 6-tetramethylpiperidone with set endpoint determination mode

Info

Publication number: CN107915673B
Application number: CN201711373652.XA
Authority: CN
Inventors: 史雅静; 王轲; 钱超; 张秀秀
Original assignee: Yantai Sunshow Chemical Technology Co ltd; Zhejiang University ZJU
Current assignee: Yantai Xinxiu New Materials Co ltd; Zhejiang University ZJU
Priority date: 2017-12-19
Filing date: 2017-12-19
Publication date: 2021-07-30
Anticipated expiration: 2037-12-19
Also published as: CN107915673A

Abstract

The invention discloses a synthesis method of 2,2,6, 6-tetramethyl piperidone with a set end point judgment mode, which comprises the following synthesis reactions: acetone and ammonia are used as raw materials, and heating reaction is carried out under the action of ammonium nitrate used as a catalyst; after the reaction is finished, distilling and recovering acetone, and rectifying after alkali washing of a distillation substrate to obtain 2,2,6, 6-tetramethyl piperidone; the pH was measured during the reaction, and when the pH remained constant within 30 minutes, it was judged that the end of the reaction was reached, and the heating was stopped to complete the reaction. The synthesis method has mild conditions, cheap and easily available raw materials and catalysts, less side reactions, simpler post-treatment and higher yield due to the reduction of the amount of by-products.

Description

Synthesis method of 2,2,6, 6-tetramethylpiperidone with set endpoint determination mode

Technical Field

The invention relates to a method for synthesizing 2,2,6, 6-tetramethyl piperidone by setting an end point judgment mode.

Background

2,2,6, 6-tetramethylpiperidone with the molecular formula C₉H₁₇NO, structural formula:

the secondary amine group of the 2,2,6, 6-tetramethyl piperidone can be converted into stable nitroxide free radical under the thermal and photo-oxidation conditions, the free radical can effectively inactivate the alkoxy free radical and alkyl free radical in the polymer, enhance the photo-oxidation resistance of the polymer and prolong the service life of the polymer, so the 2,2,6, 6-tetramethyl piperidone becomes an important raw material for preparing the hindered amine light stabilizer. At present, the literature reports that the methods for producing 2,2,6, 6-tetramethylpiperidone mainly comprise the following methods:

the method comprises the following steps: acetone and liquid ammonia are used as raw materials, acetone amine, diacetone alcohol or phorone is firstly generated, the acetone amine, the diacetone alcohol or the phorone are separated and purified, and then ammonia gas is introduced to generate the 2,2,6, 6-tetramethyl piperidone. The method has relatively more steps and low final yield of the product; however, the purity of the product 2,2,6, 6-tetramethylpiperidone is higher and the by-products are less (PCT.8705222).

The second method comprises the following steps: acetone and ammonia are used as raw materials, and 2,2,6, 6-tetramethyl piperidone is directly generated under the action of a catalyst. The method avoids the separation and purification of intermediate products, judges the reaction end point by the concentration of tetramethyl piperidone in GC, and has the defects of increased acetone polycondensation side reaction, complicated subsequent separation steps and low yield. For example, the following are several cases:

1) and patent CN201210120098.5 respectively uses ammonium nitrate and acetyl chloride as catalysts, acetone and ammonia react for 6-8 h at 70 ℃ in a reaction kettle, and the acetone: ammonia: the feeding molar ratio of the catalyst is 3.8: 2.2: 1, the yield of the final catalyst was 40% for ammonium nitrate and 30% for acetyl chloride.

When the reaction is carried out for 6-8 h, the concentration of the tetramethyl piperidone in GC is 30-40%.

2) And patent US6646127B2 uses CaY type zeolite as a catalyst, acetone, ammonia water and ammonium nitrate (as reaction raw materials) react for 2 hours at 20 ℃, and the ratio of acetone: ammonia: the feeding mol ratio of ammonium nitrate is 6: 1: 1, yield 23%.

3) Patent CN201410394675.9 with ClSO₃H modified TiO₂As a catalyst, acetone and ammonia gas in a tubular reactor are 3-9: 1, reacting at 50 ℃ and obtaining the yield of 50-60%.

Through analysis of the relevant literature, the inventors believe that the reason for the low yield of the target product in the literature is that the end point of the reaction is not reasonably controlled, so that acetone is self-condensed into a useless byproduct without an ammonia donor. The by-product can not be converted into the target product 2,2,6, 6-tetramethyl piperidone under the reaction condition.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a method for synthesizing 2,2,6, 6-tetramethylpiperidone by setting an end point judgment mode, by adopting the method, the occurrence of side reaction can be effectively prevented, and the long-chain polycondensation of acetone is reduced; the method has the advantages of simple post-treatment process, easy catalyst acquisition, mild reaction conditions, high acetone conversion rate and high yield of 2,2,6, 6-tetramethylpiperidone.

In order to solve the above technical problems, the present invention provides a method for synthesizing 2,2,6, 6-tetramethylpiperidone, wherein an end point determination mode is set, and the synthesis reaction comprises: acetone and ammonia are used as raw materials, and heating reaction is carried out under the action of ammonium nitrate used as a catalyst; after the reaction is finished, distilling and recovering acetone, and rectifying after alkali washing of a distillation substrate to obtain 2,2,6, 6-tetramethyl piperidone;

the pH was measured during the reaction, and when the pH remained constant within 30 minutes, it was judged that the end of the reaction was reached, and the heating was stopped to complete the reaction.

Remarks explanation: according to the common sense of the industry, when the change rate of the pH value within the period of 30min is less than 2%, the pH value can be judged to be kept unchanged.

Improvement of the method for synthesizing 2,2,6, 6-tetramethylpiperidone as a mode for determining an end point in the present invention: the heating reaction temperature is 60-65 ℃; acetone: liquid ammonia: the mol ratio of ammonium nitrate is 3: 1: 0.1 to 0.3 (preferably 3: 1: 0.2).

In the present invention, the end point of the reaction is determined by the pH of the reactants. Detecting the pH value of the reactant at the beginning of the reaction, wherein the reactant is stronger in alkalinity; the pH value is gradually reduced along with the reaction, and the reaction end point is reached when the pH value is kept unchanged; in this case, the acetone is just reacted with ammonia, and condensation of the remaining acetone is not started, so that side reactions are less likely to occur.

The reaction equation for synthesizing the 2,2,6, 6-tetramethyl piperidone is as follows:

the invention has the following advantages: the method has mild conditions, cheap and easily available raw materials and catalysts, less side reactions, simpler post-treatment and higher yield due to the reduction of the amount of by-products.

Detailed Description

The invention will be further described with reference to specific examples, but the scope of the invention is not limited thereto.

In the following examples, the detection instrument used was an Agilent 1790A gas chromatograph, the pre-column pressure of hydrogen and carrier gas nitrogen was 0.1MPa, the pre-column pressure of air was 0.03MPa, the temperatures of the sample injector and detector were 260 ℃, the initial column box temperature was 100 ℃, the initial time was 2min, and the rate of temperature rise was 20 ℃/min. The product concentration in the GC was calibrated by external standard.

Example 1 to a 250mL autoclave were added 87g (1.5mol) of acetone and 8g (0.1mol) of ammonium nitrate; introducing 8.5g (0.5mol) of liquid ammonia, and heating to 60 ℃ under stirring; the pH value of the reaction system is continuously detected in the reaction process, and the heating can be stopped when the pH value is not changed any more within 30 minutes, thereby stopping the reaction. At the moment, the reaction time is about 4 hours, and the pressure of the high-pressure reaction kettle is about 0.1 MPa; the concentration of the product in the GC was 48%.

After the reaction is finished, the reaction solution is filtered in a Buchner funnel, the obtained filtrate is subjected to coarse steaming at normal pressure, and the obtained light component is recycled (namely, acetone is recovered by distillation); adding flaky sodium hydroxide into the heavy component (namely, the distillation substrate) for absorbing water generated by the reaction, wherein the mass ratio of the sodium hydroxide to the crude distillation heavy component (namely, the distillation substrate) is 1: 9-10, and stirring and then standing for layering; rectifying the upper oil phase under 18mmHg, and collecting fractions at 100-110 ℃. Finally, 63g of 2,2,6, 6-tetramethylpiperidone was obtained in 81.2% yield and 96% purity.

Example 2, the reaction temperature of example 1 was changed from 60 ℃ to 65 ℃, and the rest was the same as example 1.

The final yield of 2,2,6, 6-tetramethylpiperidone was 81.8%.

Example 3, the amount of the raw materials was changed to: acetone 87g (1.5mol), 4g (0.05mol) ammonium nitrate; 8.5g (0.5mol) of liquid ammonia was introduced, and the rest was the same as in example 1.

The final yield of 2,2,6, 6-tetramethylpiperidone was 80.5%.

Example 3, the amount of the raw materials was changed to: acetone 87g (1.5mol), 12g (0.15mol) ammonium nitrate; 8.5g (0.5mol) of liquid ammonia was introduced, and the rest was the same as in example 1.

The final yield of 2,2,6, 6-tetramethylpiperidone was 81.8%.

Comparative example 1-1, the reaction time of example 1 was changed to: when the pH value is detected to be not changed any more, the reaction is continued for 2 hours to stop the reaction; that is, the reaction time was 6 hours; the concentration of the product in the GC was then 39%. The rest is equivalent to embodiment 1.

45.4g of 2,2,6, 6-tetramethylpiperidone was finally obtained in 58.2% yield.

Comparative examples 1-2, the reaction time of example 1 was changed to: the reaction was terminated 2h earlier than the reaction time of example 1; that is, the reaction time was 2 hours; the concentration of the product in the GC was then 35%. The rest is equivalent to embodiment 1.

Finally, 42.6g of 2,2,6, 6-tetramethylpiperidone was obtained in 55.2% yield.

Comparative example 2 to a 250mL reaction vessel were added 132g (2.28mol) of acetone and 48g (0.6mol) of ammonium nitrate; introducing 22.4g (1.32mol) of liquid ammonia, and heating to 70 ℃ under stirring; the pH value of the reaction system is continuously detected in the reaction process, and the heating can be stopped when the pH value is not changed any more within 30 minutes, thereby stopping the reaction. At this time, the reaction time was about 4 hours; the pressure of the high-pressure reaction kettle is 0.1 MPa.

The rest is equivalent to embodiment 1.

The final yield of 2,2,6, 6-tetramethylpiperidone was 65%.

Finally, it is also noted that the above-mentioned lists merely illustrate a few specific embodiments of the invention. It is obvious that the invention is not limited to the above embodiments, but that many variations are possible. All modifications which can be derived or suggested by a person skilled in the art from the disclosure of the present invention are to be considered within the scope of the invention.

Claims

1. The synthesis method of 2,2,6, 6-tetramethyl piperidone with the set endpoint determination mode comprises the following synthesis reactions: acetone and liquid ammonia are used as raw materials, and heating reaction is carried out under the action of ammonium nitrate used as a catalyst; after the reaction is finished, distilling and recovering acetone, and rectifying after alkali washing of a distillation substrate to obtain 2,2,6, 6-tetramethyl piperidone;

the method is characterized in that: detecting the pH value in the reaction process, and judging that the reaction end point is reached when the pH value is kept unchanged within 30 minutes, so as to stop heating to finish the reaction;

the heating reaction temperature is 60-65 ℃; acetone: liquid ammonia: ammonium nitrate in a molar ratio = 3: 1: 0.2.

2. the method for synthesizing 2,2,6, 6-tetramethylpiperidone with a set endpoint determination as defined in claim 1, which comprises:

adding 1.5mol of acetone and 0.1mol of ammonium nitrate into a 250mL high-pressure reaction kettle; introducing 0.5mol of liquid ammonia, and heating to 60 ℃ under stirring; continuously detecting the pH value of the reaction system in the reaction process, and stopping heating when the pH value is not changed any more within 30 minutes so as to stop the reaction; at the moment, the reaction time is 4 hours, and the pressure of the high-pressure reaction kettle is 0.1 MPa; the concentration of the product in the GC was 48%.