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OXIDATIVE ESTERIFICATION

IP.com Disclosure Number: IPCOM000237913D
Publication Date: 2014-Jul-21
Document File: 3 page(s) / 60K

Publishing Venue

The IP.com Prior Art Database

Abstract

Polymerization inhibitors are disclosed for use in the production of esters via the reaction of aldehydes with alcohols and oxygen utilizing a palladium-containing catalyst.

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This is the abbreviated version, containing approximately 54% of the total text.

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OXIDATIVE ESTERIFICATION

     It is known that aldehydes can be reacted with alcohols and oxygen utilizing a palladium-containing catalyst in order to produce esters. For example, the conversion of methacrolein to methyl methacrylate by reacting methacrolein, methanol, and molecular oxygen over a supported palladium-containing catalyst to form methyl methacrylate and water has been discussed in the literature. This reaction can progress by introducing air into a liquid- phase containing methacrolein and methanol in the presence of a heterogeneous palladium- containing catalyst. Both methacrolein and methyl methacrylate are monomers that can polymerize if not properly inhibited.

     The use of certain inhibitors, such as 4-hydroxy-TEMPO, 1, (CAS Registry Number: 2226- 96-2) and/or its derivatives, in this reaction system is advantageous, since 4-hydroxy-TEMPO and derivatives do not appear to deleteriously affect catalyst performance under conditions where other types of inhibitors may do so. Aside from 4-hydroxy-TEMPO itself, examples of derivatives of 1 include, acetylated 4-hydroxy TEMPO of a general form 2; one example being 4- (acetyloxy)-2,2,6,6 tetramethylpiperidine-N-oxyl, CAS Registry Number 6599-87-7, where R=methyl in structure 2. Other examples of 2 include both compounds with R groups having longer chain alkyl hydrocarbons, which can be straight chained or branched, containing anywhere from 1 to 15 carbons, as well as 4-hydroxy TEMPO diesters such as 3 where n equals an integer from 1 to
16.

     Additional examples of 4-hydroxy-TEMPO derivatives include 4-oxo TEMPO (CAS Number 2896-70-0), structure 4, and alkyl ethers of 4-hydroxy-TEMPO, 5, with straight chain or branched hydrocarbon moieties having from 1 to 15 carbon atoms.

     Further illustrations of 4-hydroxy TEMPO derivatives include molecules where the oxygen at the 4- position of 4-hydroxy TEMPO may be replaced by a heteroatom such as nitrogen as in 6a where the R1 and R2 groups on the nitrogen independently equal hydrogen, alkyl, aryl or combinations thereof and 6b where the nitrogen at the 4-position is N-acetylated such as in 4-acetylamino-2,2,6,6-tetramethylpiperidine-N-oxyl, CAS Number 14691-89-5 where R1 equals hydrogen and R2 equals methyl. In other examples of 6b, R1 equals hydrogen and R2 can be a linear or branched aliphatic hydrocarbon moiety ranging from C1 to C15, or aromatic.


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O

R

OH O

   O H2
C n

O O

O O

O

O O

R = C1 - C15 hydrocarbon linear or branched

N

N

n =1-16

N

N

1

2

3

R

O O

O O

     R2 R1

N

R = C1 - C15 hydrocarbon linear or branched

R1,R2 = H, alkyl, aryl

N

N

N

O

6a

4

5

O

R2

R1

N

O

  N N

4

O - R+

5

6

1 2

N

3 R1 = H,
R
2 = alkyl C1 -...