CA1214174A - Acetal esters - Google Patents

Abstract

ACETAL ESTERS

ABSTRACT OF THE DISCLOSURE

Esters of monoacetals of pentaerythritol. The monoacetals result from the reaction of a 4-hydroxyphenylpropionaldehyde and pentaerythritol, and the further reaction of this monoacetal with either of two particular acid chlorides yields the esters of the invention. These esters are useful, in small propor-tions, to stabilize polymer compositions, especially olefin polymers,

Description

0791 2l~-M ~2~

ACETAL E STE RS

This invention relates to certain esters of monoacetals of pentaerythritol. More particularly, it relates to such esters as contain a phenolic group within their structure. It also relates to a process by which such esters may be prepared.
The esters herein are useful as polymer additives. They are especially useful in olefin polymer compositions, e.g., polypropylene compositions, where they act to impart thermal stabllity to such compositions. They are useful also as intermediates in the preparation of phenolic ethers which in turn are useful as plasticizers in polyester resins. Generally, olefin polymer compositions are vulnerable to deterioration of physical and chemical properties during manufacture, storage, processing and use. To overcome such deterioration, or at least to inhibit it, there have been developed additive systems which act to stabilize these polymers with respect to physical and chemical degradation caused by exposure to ordinary environ-mental conditions. All of these additive systems, howeYer, while effective for their intended purpose, are characterized by one or more shortcomings.
Olefin polymers are especially susceptible to oxidative degradation. The relat;vely high temperatures required for their customary processing procedures such as roll milling, injection molding9 extrusion and the like, invariably promote oxidation because these processes are carried out under ordinary atmospheric conditions, i.e., they are exposed to the oxygen of the aemosphere.
The significance of polymer oxidation lies in the adverse effec~ i~ has on the rheology, morphology, color, clarity, 910s5 and other physical properties. Impact strength may be lose; the surface may become cracked or cra~ed. Even a darkening of the color may provide a sufficient aesthetic dis-advantage as to render the olefin polymer composition unsuitable for its intended use.
U.S. 3,948,946 (Hofer et al.) shows acetals of hydroxy-benzaldehydes. The acetals are the reaction products of 2,2-dimethyl-1,3-propanediol, pentaerythritol, ethylene glycol, 1,2-ethanedithiol, toluene-3,4-dithiol, etc. That is, the alcohol precursor is polyhydric. The reaction o~ pentaeryth-ritol, however, is carried out ~o completion, i.e., all of the aliphatic hydroxy groups are acetalized. The acetals are said to be effective stabilizers for organ;c materials.
U.S. I~,013,619 (Schmidt) shows acetals of certain hydroxy-phenylacetaldehydes and hydroxyphenylpropionaldehydes, in some instances (see Columns 16 and 17), with pentaerythritol residues.
The acetals are either monoacetals or diacetals, but the mono-acetals do not contain unreacted aliphatif hydroxy groups. The acetals are said to be effective heat stabilizers in synthetic resin compositions.
U.S. 4,151,211 (Hechenbleikner et al.) shows acetals of 4-hydroxyphenylpropionaldehydes and such hydroxy or mercapto compounds as pentaerythritol, dodecyl mercaptan and various other acetalizing reactants, as well as their use in stabili~ing polypropylene. None of the acetals, however, contain unreacted aliphatic hydroxy groups.
French Patent No. 2,301,558 shows certain diacetals of pentaerythritol and 3,5-ditertiarybutyl-4-hydroxyphenyl propionaldehyde and 3,5-ditertiarybutylbenzaldehyde.
The invention of this application i~ an ester of a pentaerythritol monoacetal haviny the st.ucture . ~ .

7~

HO ~ CH2 ~ C~I ~ C(CH20)2(A-X)p where R is alkyl, cycloalkyl or aralkyl having 3-10 carbon atoms, Rl is alkyl of 1-6 carbon atoms, R2 is lower alkyl or hydrogen, A is ll or P-0, X is an organic radical, n is 0-3, and p is ~-2. C
The invention also includes the process of preparing such esters c~mprising reacting a monoacetal of pentaerythritol having the structure ~ CH2 ~ CH ~ C(CH20H)2 where R is alkyl r cycloalkyl or aralkyl having 3-lO carbon atoms, Rl is alkyl oF 1-6 carbon atoms and R2 is lower alkyl or hydro-gen, with an ester-forming compou~d having the structure Clm-A-X where m is 1 or 2, A is 1l or P-O, X is an organic radtcal and n is 0-3. The term "lower alkyl" denotes an alkyl group having 1-4 carbon atoms.
Illus~rative species of R include methyl, ethyl, isopropyl, tertiarybu~yl, tertiaryamyl, 2,2'-dimethylbutyl, cyclopentyl, cyclohexyl, 2 methylcyclohexyl, ben~yl and phenylethyl9 illus-trative species Of Rl include methyl, ethyl, isopropyl, tertiarybutyl, tertiaryamyl and 2,2'-dimethylbutyl; illustra-tiYe species of R2 include methyl, ethyl, n-propyl, isobutyl and hydrogen. Preferably, at least one of R and Rl Is a bulky group, e.g., tertiarybutyl or cyclohexyl.

The organic radical X is an aromatic radical, i.e., it contains a henzene ring. It may be a substituted aryl group, i.e., an alkylphenyl group (where the alkyl has 1-6 carbons) such as 4-tertiarybutylphenyl, 2,4-ditertiarybutylphenyl or ~,6-diisopropylphenyl; or a hydroxyphenyl group such as 4-hydroxy-2-methyl-3-tertiarybutylphenyl, 4-hydroxy-2,3-ditertiary~tylphenyl, 4-hydroxy-3,5-ditertiarybutylphenyl or 4-hydroxy-2-tertiarybutyl-5-n-octylphenyl. The aromatic radical may be one which is attached directly to the A group, i.e., through a benzenoid carbon atom, or it may be attached through an aliphatic carbon atoms, e.g., benzyl, 2-pheny1ethyl,

2-(4-hydroxyphenyl)ethyl and 2-(4-hydroxy-3,5-ditertiarybutyl-phenyl)ethyl.
In general, X is phenyl, alkylphenyl, or (hydroxyphenyl)-~5 alkyl, where the alkyl group(s) in each case have 1-6 carbon atoms.
The process o~ the invention involves reactlng the above pentaerythritol acetal with the acid chloride under such con-ditions as to cause the evolution of hydrogen chloride. The reaction is slightly exothermic and it is accordingly advisable to employ external cooling to control the reaction. Stoichio-metric quantities o~ the reactants should be employed for best results, i.e., two mols of carboxylic acid chloride per mol of pentaerythritol monoacetal, or one mol o~ the dichlorophosphite per mol of pentaerythritol monoacetal.
A hydrogen chloride acceptor is employed, usually a tertiary aliphatic amine such as triethylamine or tri-n-butylamine, i.e., one having 3-12 carbon atoms, and the reaction is best carried out in a solvent. Typical so1vents 3a include toluene, dioxane, benzene, and the like. Any inert solvent is suitable. The temperature of the reaction ordinarily is within the range of ~rom about 10C t~ about 100C.

The reactants, solvent and hydrogenchloride acceptor are mixed, stirred until reaction is complete and the desired solid product separated. If a pure product is desired, crystalliza-tion from a hot aliphatic hydrocarbon (such as hexane) usually will serve that purpose.
The process is illustrated by the following examples.

A mixture of 13.0 9. (0.034 mol) of the monoacetal of pentaerythritol and 3-(4-hydroxy-3,5-ditertiarybutylphenyl)-propionaldehyde, 17.6 9. (o.066 mol) of 4-hydroxy-3,5-ditertiarybutyl-benzoyl chloride and 115 ml. of toluene is stirred in an ice bath until the temperature is about 3 C
whereupon ]1.5 ml. (8.38 g. - 0.083 mol) of triethylamine is added. An exothermal reaction occurs and the temperature rises to 30C. Stirring is continued for 45 minutes then the mixture is heated to 80C and filtered. The filtrate is s~ripped to a residue weighing 33.0 9.; it is crystallized 2Q from hot hexane to yield 11.75 9. (42.5~ of the theory) of white crystals, M.P.~ 123-7C.

E~AMPLE_2 A mixture of 9.59 9. (0.025 mol) of the monoacetal of pentaerythritol and 3-(4'-hydroxy-3',5'-ditertiarybutyl-phenyl)propionaldehyde, 10.4 ml. (7.6 9. - 0.107 mol) of triethylamine and 90 ml. of dioxane is prepared and stirred until all is in solution; a solution of 15 9. (0.051 mol) 30 of 3-~4'-hydroxy-3',5'-ditertiarybutylphenyl)propionyl chloride is added slowly with external cooiing and stirring is continued for 90 minutes at room temperature after all is added~ The temperature is raised to 80C and held there -for 90 minutes, then the mixture is filtered. The filtrate is evaporated to dryness and the residue crystallized from hot hexane to yield 16.15 9. (71~ of ~he theory) of the desired diester, M.P., 95-100C.

To a stirred mixture of 9.5 g. (0.025 mol) of the mono-acetal of pentaerythritol and 3-(4'-hydroxy-3',5'-ditertiary-butylphenyl~propionaldehyde, 10 ml. (7.3 9. - 0.103 mol) of triethylamine and 100 ml. of toluene there is added, with stirring, 7.68 g. (0.025 mol) of dichloro 2,4-ditertiary-butylphenyl phosphite. An exothermic reaction ensues and the temperature of the reaction is kept below 40C by means of an ice bath. When the reaction has subsided the product mixture is filtered and the filtrate is evaporated to 15.0 9.
of a yellow, gummy residue. Crystallization from hot heptane yields 12.5 9. (81~ of the theory) of a light yellow solid, 20 M.P., 138-140C.

The procedure of Example 2 is repeated except that ~hec~ ~_ monoacetal reactant is derived from 3-(2',3'-dimethyl , ~ tertiarybutylphenyl)propionaldehyde.
., ~

The procedure of Example 3 is repeated except that the phosphite reactant is d;chloro-2,6-diter~iarybutylphenyl phosphtte.

079124-M ~2~7~

The acetal esters of the invention are, as indicated earlier herein, useful in olefin polymer composit;ons. They generally are present in such compositions in combination with a dialkyl thiodipropionate where the alkyl group is one having 10-20 carbon atoms; distearyl dithiopropionate is preferred.
The acetal ester is used in concentrations ranging from about 0.01% to about 1.0%; the dialkyl thiodipropionate is used in concentrations ranging from about 0.05~ to about 0.75%.
The efficacy of the acetal~esters herein as polymer stabilizers is shown by the data set out in the Table below.
The data is derived from thermal stability tests carried out at 150C. Each sample is heated at this temperature and inspected at periodic intervals until it fails (as evidenced by embrittlement, crazing and/or cracking). The samples each consist of polypropylene containing O.tO pph (parts per hundred parts of resin), calcium stearate and other additives as shown. Color ratings ~Hunter L-b) are assigned to each sample prior to (1nitial) and after ~Final) 600 hours at 150C.
The stabili~y rating is measured as the number of hours required for failure, and is the average of these sa~ples.

Color Acetal-Ester (pph) DSTDP (pph) Initial Final Stability Product of Example 1 0.03 0.25 75.874.o 0.05 0.20 ~ - 1264 0.05 0.30 ---- ---- 136~
0.075 0.25 75.673.9 1632 3Q 0.075 0.30 -~ 1800 ~2~7~

Color Acetal-Ester (pph) DSTDP (pph) Initial Final Stability Product of Example 20.03 0.25 75.674.0 1304 0.05 0.20 ~ - 1464 0.05 0.30 ~ 1664 0.75 0.25 7~.872.1 1632 35 ~~~~~~~~ 1824 Product of Example 30.05 0.25 74.3 ----0.10 0.25 7~.567.9 Product of Example 40.05 0.25 1416 Product of Example 50.05 0.25 76.1 ---~
0.10 0.25 74.370.

None ---- 0.25 168 All parts and percentages herein, unless otherwise expressly stated, are by weight.

Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the preparation of esters of pentaerythritol monoacetal, comprising reacting a monoacetal of pentaerythritol of general formula:

wherein n is zero, one, 2 or 3, R represents a group selected from C3-10alkyl, C3-10cycloalkyl and C3-10 aralkyl, R represents Cl-6 alkyl and R2 represents a group selected from H and lower-alkyl, with an ester-forming compound of general formula:
Clm-A-X, wherein m is one or 2, A represents a group selected from -C(O)- and -PO-, and X represents a group selected from phenyl, alkylphenyl and (hydroxphenyl)alkyl.

2. The process of claim 1, wherein R and R1 are each tertiary butyl and R2 is hydrogen.

3. The process of claim 1, wherein R is tertiary butyl and R and R2 are each methyl.

4. The process of claim 1, 2 or 3, wherein A is -C(O)-.

5. The process of claim 1, 2 or 3, wherein A is -PO-.

6. The process of claim 1, 2 or 3, wherein X is phenyl.

7. The process of claim 1, 2 or 3, wherein X is an alkyphenyl.

8. The process of claim 1, 2 or 3, wherein X is a (hydroxyphenyl)alkyl.

9. A pentaerythritol monoacetal ester of general formula.

wherein n, A, R, Rl, R2 and X are as defined in claim 1 and p is one or 2.

10. The ester of claim 9, wherein A is -C(O)-.

11. The ester of claim 9, wherein A is -PO-.

12. The ester of claim 9, 10 or 11, wherein X is phenyl.

13. The ester of claim 9, 10 or 11, wherein X is an alkylphenyl.

14 A The ester of claim 9, 10 or 11, wherein X is a (hydroxyphenyl)alkyl.