WO2018010055A1

WO2018010055A1 - Preparation of sorbate

Info

Publication number: WO2018010055A1
Application number: PCT/CN2016/089591
Authority: WO
Inventors: Selvanathan Arumugam; John ELL; John W. Hull, Jr.; Bo LV; Brandon ROWE; Wei Wang; Steven Zhang
Original assignee: Dow Global Technologies Llc; Rohm And Haas Company
Priority date: 2016-07-11
Filing date: 2016-07-11
Publication date: 2018-01-18

Abstract

Provided is a process for preparing a sorbate by contacting sorbic acid with an alcohol, a diol, a triol, a C₂-C₄-alkylene oxide, or a mono-or diglycidyl ether in a reactor under conditions sufficient to form the sorbate. The reaction is carried out under an atmosphere of reduced oxygen and in the substantial absence of a free radical inhibitor.

Description

[Title established by the ISA under Rule 37.2] PREPARATION OF SORBATE

The present invention relates to the preparation of a sorbate without the use of an inhibitor. The sorbate is useful as a coalescent in coatings formulations.

Recent environmental regulations around the globe are driving the push toward materials with very low or no odor and low volatile organic chemicals (VOCs) in the architectural coatings market. Balancing VOCs against desired paint performance attributes is a continuing challenge.

Paint formulations comprise either a low T_g polymer latex that forms film with little or no coalescent, or a high T_g latex that forms film with the aid of a coalescent. Formulations containing low T_g polymers generally give coatings having a soft and tacky feel and poor durability. Formulations using high-T_g polymers, on the other hand, require either permanent (nonvolatile) coalescents or volatile coalescents； permanent coalescents are known to adversely affect the hardness performance of the consequent coating； volatile coalescents such as Texanol, on the other hand, may give acceptable hardness performance –for example, a

hardness of ～ 20 s at 28 days for a typical semigloss paint –but are undesirable for their volatility.

Both low temperature film formation and film hardness can be achieved by using a reactive coalescent. For example, WO 2007/094922 describes the use of a bis-allylic unsaturated fatty acid ester as a reactive coalescent. Unfortunately, the described coalescent does not yield the desired hardness performance properties for the consequent coating.

A particularly attractive class of coalescents is the sorbate, especially the disorbate, which has a particularly low VOC. Sorbates are conventionally prepared by esterification of an alcohol and sorbic acid in an aprotic solvent and at a temperature above 100 ℃. Inasmuch as the reactive nature of sorbic acid renders it prone to forming polymeric byproducts under these harsh reactive conditions, conventional methods describe the use of a free radical inhibitor to suppress the formation of these undesirable byproducts. Nevertheless, the presence of a free radical inhibitor in the consequent coating composition may adversely impact the cure rate of the sorbate, since cure rate is augmented by the presence of free radicals.

It would therefore be an advantage in the art of low VOC coalescents to discover a way to prepare a sorbate, particularly a low VOC sorbate, without a free radical inhibitor.

Summary of the Invention

The present invention addresses a need in the art by providing a process comprising the step of contacting sorbic acid with an alcohol, a diol, a triol, a C₂-C₄-alkylene oxide, or a mono-or diglycidyl ether in a reactor under conditions sufficient to form a sorbate； wherein the process is carried out in the substantial absence of a free radical inhibitor； and wherein the reactor has a headspace with less than 5％v/v oxygen.

The process of the present invention provides a way to form sorbates in the substantial absence of free radical inhibitors, resulting in a coalescent with a faster curing rate in a coatings formulation.

Detailed Description of the Invention

The present invention addresses a need in the art by providing a process comprising the step of contacting sorbic acid with an alcohol, a diol, a triol, a C₂-C₄-alkylene oxide, or a mono-or diglycidyl ether in a reactor under conditions sufficient to form a sorbate, wherein the process is carried out in the substantial absence of a free radical inhibitor； and wherein the reactor has a headspace with less than 5％v/v oxygen. As used herein, “sorbate” refers to a mono-, di-, or trisorbate. Preferred sorbates are disorbates.

Examples of suitable alcohols, diols, and triols include octanol, decanol, diethylene glycol, triethylene glycol, glycerol, 2-butoxyethan-1-ol, 2- (2-butoxyethoxy) ethan-1-ol, 2- (2- (2-butoxypropoxy) propoxy) propan-1-ol； suitable alkylene oxides include ethylene oxide, propylene oxide, butylene oxide, and oxiran-2-ylmethanol； and suitable glycidyl ethers include phenyl glycidyl ether and allyl glycidyl ether. Preferred compounds that are used to react with sorbic acid are diols, preferably triethylene glycol.

The primary products of the reaction of sorbic acid and triethylene glycol are triethylene glycol disorbate and triethylene glycol monosorbate, illustrated are as follows:

The reaction is preferably carried at an internal temperature (i.e., the temperature of the contents of the reactor) in the range of from 90 ℃, preferably from 100 ℃, and more preferably from 110 ℃, to 170 ℃, preferably to 160 ℃, more preferably to 150 ℃, and most preferably to 140 ℃. Preferably, the solvent is immiscible with water, has a boiling point in the range of 100 ℃ and 180 ℃, and has a density less than that of water. Examples of suitable solvents include toluene, xylene, chlorobenzene, ethyl benzene, and dibutyl ether, with toluene being preferred.

The amount of solvent used in the reaction is generally in the range of from 0.25, more preferably from 0.5, and most preferably from 0.75 times, to 4, more preferably to 2, and most preferably to 1.25 times the weight of sorbic acid and triethylene glycol used.

The concentration of strong acid catalyst used to promote the reaction is typically in the range of from 0.1, preferably from 0.5, more preferably from 1, and most preferably from 2 weight percent, to 10, preferably to 4, and more preferably to 3 weight percent, based on the weight of sorbic acid. Examples of suitable strong acids include sulfuric acid, toluene sulfonic acid, and sulfamic acid. It has been found to be advantageous to dilute sulfuric acid in a solvent to reduce the formation of undesirable color bodies in the final product. A preferred w/w ratio of solvent to sulfuric acid is in the range of from 5: 1 to 20: 1.

The mole-to-mole ratio of sorbic acid to triethylene glycol is preferably from 4: 1, more preferably from 3: 1, more preferably from 2.5: 1, and most preferably from 2.2: 1, to 2.0: 1.

The reaction also advantageously includes a substantial absence of a free radical inhibitor such as dibutylhydroxytoluene (BHT) , (2, 2, 6, 6-tetramethylpiperidinyl-1-yl) oxyl (TEMPO) , 4-hydroxy-TEMPO, hydroquinone, p-methoxyhydroquinone, t-butyl-p-hydroquinone, t-butyl-4-hydroxyanisoles, and 4-t-butyl catechol. As used herein, a substantial absence of free radical inhibitor refers to less than 20 ppm, preferably less than 10 ppm, more preferably less than 1 ppm, and most preferably 0 ppm of a free radical inhibitor.

The preference for a solvent that is high boiling, aprotic, water-immiscible, and less dense than water arises from the desirability to remove water that is formed during the course of the reaction and recycling back solvent. An apparatus particularly suitable for this purpose is a Dean-Stark trap.

In an especially preferred method of preparing the high purity disorbate, sorbic acid and triethylene glycol (at about a 2.2: 1 mole-to-mole ratio) are placed a flask equipped with a Dean-Stark trap along with toluene. The mixture is advantageously sparged with an inert gas such as nitrogen to reduce the oxygen concentration in the headspace and in the mixture and the contents of the flask are stirred and heated to dissolve the acid. A mixture of sulfuric acid in toluene (about a 1: 1 weight ratio of toluene to reactants) is added slowly to the flask, whereupon the temperature of the mixture is raised to 120 ℃ to 130 ℃. The reaction proceeds until the condensation of water in the Dean-Stark trap proceeds to substantial completion, typically from about 1 to 24 hours.

It has been surprisingly discovered that lowering the concentration of oxygen from the headspace of the reactor, with concomitant reduction of oxygen in the solvent, allows the reaction to proceed in high yield and purity without formation of gel. Significantly, when the oxygen concentration in the headspace of the reactor is less than 5％, preferably less than 3％, more preferably less than 2％v/v, more preferably less than 1％v/v, and most preferably less than 0.1％v/v, the reaction can be carried out efficiently in the substantial absence of a free radical inhibitor. Exclusion of free radical inhibitor from the reaction is important because it has been found that residual free radical inhibitors in the sorbate product have an adverse impact on the cure rate of paint coatings； therefore, the process of the present invention represents an advance in the art by providing a way to make a high purity, high yield sorbate in the substantial absence of a free radical inhibitor.

The following examples demonstrate the preparation of a high purity, gel-free triethylene glycol disorbate that gives an improved cure profile of a paint coating.

Examples

Example 1 –Preparation of Triethylene Glycol Disorbate with Reduced Headspace Oxygen

To a 500-mL three neck flask equipped with a Dean-Stark trap was added sorbic acid (82.13 g) , triethylene glycol (50 g) , sulfuric acid (0.1 molar equivalent to triethylene glycol) , and toluene (140 mL) . The reaction mixture was sparged with nitrogen to reduce the headspace oxygen concentration to 2％v/v. The mixture was heated to 80 ℃ under the desired concentration of headspace O₂ with stirring until all the solid acid dissolved, then further heated to an internal pot temperature of 114 ℃. The reaction proceeded until water ceased condensing in the Dean-Stark apparatus from the toluene/water heterogeneous zoetrope. The reactor and contents were cooled to room temperature upon completion of the reaction and the triethylene glycol disorbate was isolated.

Comparative Example 1 –Preparation of Triethylene Glycol Disorbate

The synthesis was prepared in substantially the same manner as described in Example 1 except that ambient atmospheric conditions were used (～21％oxygen) .

The stability of triethylene disorbate (TEG-Disorbate) was measured at 60 ℃ for 14 h for concentrations of headspace oxygen varying from 0％to 21％. Analytical grade calibrated gas cylinders were used to create the desired headspace. Oxygen concentration can be verified using a Cole-Parmer Model No. 10360-70 benchtop headspace O₂ analyzer with electrochemical O₂ sensors. The results are summarized in Table 1.

Table 1 –TEG Disorbate Stability at Various O₂ Headspace Concentrations

Example No.	Head Space O₂ Conc (v/v ％)	TEG-Disorbate Stability
Comp Ex 1	Air (21％)	Gelled
Comp Ex 2	10％in N₂	Gelled
Comp Ex 3	5％in N₂	Gelled
Example 1	2％in N₂	Stable
Example 2	0％in N₂	Stable

As Table 1 illustrates, gelation occurs at concentrations of 5％or greater. It has also be discovered that the degree of gelation increases while yields of the desired disorbate decrease with increasing concentrations of oxygen in the reaction mixture.

As Table 2 illustrates, acceptable yields of the disorbate occur at a 5％oxygen headspace concentration (which is why less than 5％is considered to be the upper limit of acceptability for oxygen headspace concentration) in but undesirable color bodies form at this concentration. The color was measured by preparing a 50 weight ％solution of the disorbate in isopropanol and measuring the absorbance at 400 nm with a 1-cm path length.

Table 2 –Yield and Color of Disorbate Versus O₂ Headspace Concentration

Example No	Head Space O₂ Conc (v/v ％)	TEG-Disorbate Yield	Absorbance
Comp Ex. 3	5％in N₂	87.6	1.50
Example 2	0％in N₂	96.8	0.35

As Table 2 shows, removal of oxygen from the headspace of the reactor gives the desired disorbate in high yields with substantially lower levels of color bodies.

Paints were prepared with the TEG Disorbate as prepared in Example 2 and TEG Disorbates prepared with various amounts of the inhibitor BHT as follows. The TEG Disorbate (1.56 g) was added to the base paint (100 g) and stirred using overhead mixing. A thin film of the formulation (～ 10 mil, ～250 μm) was drawn down on testing substrates and allowed to dry under ambient conditions.

hardness, one of the key performance attributes of a paint, can be used to measure coalescent cure rates during paint drying process.

hardness measurements were completed using a TQC Pendulum Hardness Tester, Model SP0500. The coatings used for

measurements were made on Al substrates with a 10-mil blade gap.

The master paint formulation is illustrated in Table 3 and 7-day

hardness results are shown in Table 4. Paint Example 2 refers to the paint formulation using the TEG-Disorbate as prepared in Example 2.

Table 3 –Master Paint Formulation

Stage	Materials	Wt (g)
Grind
	TiPure R-746 TiO₂	452.8
	Water	30
	BYK-024 Defoamer	3
	TRITON^TM X-100 Surfactant	6.6
	TAMOL^TM 2002 Dispersant	3
	ACRYSOL^TM RM-2020 NPR Thickener	30
	Grind Sub-total	644.41
Let-down
	RHOPLEX^TM HG-95P Emulsion Polymer	882.7
	BYK-024 Defoamer	1.5
	Ammonia (28％)	0.38
	ACRYSOL^TM RM-2020 NPR Thickener	35.8
	ACRYSOL^TM RM-8W Thickener	2.67
	Water	137.06
	Total	4162.2

TRITON, TAMOL, RHOPLEX, and ACRYSOL are all Trademarks of The Dow Chemical Company or its Affiliates.

It is well known that concentrations of free radical inhibitors such as BHT need to be above 5000 ppm to be effective in preventing the formation of higher molecular weight byproducts. As Table 4 shows, BHT levels even as low as 1000 ppm, which would be ineffective to prevent gel formation, contribute to a marked reduction in

hardness.

Table 4 –

Hardness Versus BHT Inhibitor Levels Used in Preparing TEG-Disorbate

The above results demonstrate that reducing concentrations of oxygen in the headspace of the reactor results in high yields of a sorbate with no gel and significantly reduced color body formation； moreover, the ability to make sorbates without any free radical inhibitors increases the cure profile of a paint formulation.

Claims

A process comprising the step of contacting sorbic acid with an alcohol, a diol, a triol, a C₂-C₄-alkylene oxide, or a mono-or diglycidyl ether in a reactor under conditions sufficient to form a sorbate； wherein the process is carried out in the substantial absence of a free radical inhibitor； and wherein the reactor has a headspace with less than 5％ v/v oxygen.
The process of Claim 1 wherein the sorbic acid is contacted with the alcohol, the diol, the triol, the C₂-C₄-alkylene oxide, or the mono-or diglycidyl ether in the presence of a strong acid catalyst at a temperature in the range of from 90℃ to 170℃.
The process of Claim 2 which is carried out in the presence of a solvent that is water-immiscible, has a boiling point between 100℃ and 180℃, and forms an azeotrope with water.
The process of Claim 3 which further includes the step of distilling the solvent and water from the reactor during the course of the reaction.
The process of any of Claims 2 to 4 wherein the sorbic acid is contacted with triethylene glycol to form triethylene glycol disorbate, wherein the strong acid catalyst is sulfuric acid or toluene sulfonic acid.
The process of any of Claims 1 to 5 wherein the concentration of the free radical inhibitor in the reaction mixture is less than 10 ppm.
The process of Claim 6 wherein the concentration of oxygen in the headspace of the reaction is less than 3％ v/v and the concentration of the free radical inhibitor is less than 1 ppm.
The process of Claim 6 wherein the concentration of oxygen in the headspace of the reaction is less than 1％ v/v and the concentration of the free radical inhibitor is 0.