I
JACOB C. MINOR and RAY V. LAWRENCE Naval Stores Station, U. S.' Department of Agriculture, Olustee, Fla.
Esterification of Methylolated Rosin This method for preparing improved rosin-based varnishes has several advantages -economy, faster drying, and better water resistance
1
MPROVED ROSIN-BASED varnishes can be prepared by methylolating rosin with formaldehyde. This produces a mixture of bifunctional hydroxy resin acids which, when inter- or trans-esterified with drying oils, yields low acid number, high viscosity products which can be further neutralized by glycerol esterification. This new procedure offers several advantages over conventional ester gumlinseed oil processes-varnish films dry faster and have superior water resistance. Also, economies are realizedcooking time is shorter and instead of being converted to an ester gum prior to cooking, the resin is processed directly in a single batch operation.
Intermittent or slow stirring avoided excess loss of formaldehyde, and when the reaction was completed (1.0 to 1.5 hours) the temperature was raised to 200' to 285' C., depending on the reflux temperature of the acids. Esterification was carried out by one of two procedures, using a slow stream of inert cover gas (15 to 20 ml. per minute) to minimize oxidation and remove water of reaction. A mild vacuum (10 to 15 inches) was also effective in removing water. Samples were taken a t hourly intervals. Color grade and acid numbers were determined by ASTM
methods, and viscosity by a Gardner bubble viscometer a t 25' C. In procedure 1, one equivalent of fatty acid was added to the hot methylolated rosin and the temperature was increased to 275' to 280' C. (or to the reflux temperature of the fatty acid) an4 held for 4 hours. The resin-acid carboxyl group was then esterified by adding 1 equivalent of glycerol, based on the acid number of the reaction product, and heating the mixture a t 285' f 5' C. for an additional 2 hours. This reduced the acid number to 10 to 15.
Experimental
WW gum rosin (100 parts) and 15 to 20 parts of paraformaldehyde, added to a three-necked reaction flask, was raised to a temperature of 115' C.
Literature Background Subject
Reference
Addition and condensation reactions of formaldehyde with ethylenic hydrocarbons (1,8) Pkocess for hardening rosin with formaldehyde (45) Preparation of some fatty acid esters of methylolated rosin by acid exchange (8) Acetic acid ester of methylolated rosin can form a rosin polymer by acid exchange (2) Esterification of methylolated resin at temperatures below 225O C. (4)
C17H31 0 II e-cl 7 H 31
This is the probable structure of glyceryl esters from the dilinoleate of rnethylolated abietic acid VOL. 50, NO. 8
AUGUST 1958
1 127
6C
cn W
0
METHYLOLATED A. 0
ROSIN
B. x UNMETHY LOLATED R OSlN C.
v,
The Same Materials Were Used for Both Procedures
LINSEED OIL, G A L 12.5 25.
Abietic acid
Gum rosin, W W
12.5 25.
D. Q
grade
/"
a I
A
Refined linseed oil Linseed oil acid mixtures Tung oil
40
z
I-
Saturated and other unsaturated oils
Y,
Prepared by quartersalt method (7) Acid No., 168; ring and ball softening point, 72' C. Acid No., 1.8 Prepared by glycerolalkali sapon. ( 6 ) From U. S. Dept, Agr., New Orleans, La. Reagent grade
0
u
2
20
>
$ 6
I
0'
I
I
I
60 I20 REACTION TIME
I
-
I
I
I
240
I80 MINUTES
Figure 1. Viscosity increases more for products from methylolated rosin and linseed oil than those from unmethylolated rosin
8
H29 -0-C-R'
R
I
HL
II
Figure 2. Possible course of reaction between methylolated rosin and linseed oil i s shown b y this schematic arrangement
Table I. Esterification Products of Methylolated Rosin and Fatty Acids" Pts./100 Pts. Gum Rosin M ~ ~ . Esterifying Acid
Acid 32 64 39 57 57
Acetic Caproic Pelargonic" Pelargonic Stearic
88
Paraformaldehyde 15 20 20 15 15 20
React. Temp., ___ C. 0 . 0 hr. Saturated 330 200 372 200 234 205 260 232 209 260 173 275
Acid No. 1.0 hr. 2.0 hr. 260 265 163 182 165 125
Unsaturated 188 139 94 20 280 Linseed acids' 153 172 94 20 280 Linseed acids 166 124 94 20 280 Linoleic 177 129 94 20 280 Oleic 127 280 165 94 20 Tung oil acids a Procedure 1. Excess acid removed by sparging with steam. Abietic acid was methylolated and used in lieu of rosin. ~~
1 128
~
INDUSTRIAL AND ENGINEERING CHEMISTRY
Procedure 2 differed in that tung or linseed oil was used and the temperature was increased to 280' i: 5' C. The interesterification approached equilibrium in 3 to 4 hours and the resulting acid number was usually between 25 and 50. Adding glycerol brought the acid number down to 10 to 15 and gave a varnish base having a viscosity of about 140 poises. When 200 grams of rosin was heated a t 275' C. for 3 hours, its acid number decreased 24 units. This agrees with previous results (77). When a similar sample was heated with 35 grams of paraformaldehyde for 11/2 hours a t 110' to 120' C. and the excess formaldehyde removed by blowing with nitrogen, its acid number decreased from 168 to 146. This decrease with a corresponding increase in weight indicated that about 30 grams of paraformaldehyde had reacted with the rosin. When ihis methylolated rosin was heated a t 275' C. for 3 hours, the acid number decreased from 146 to 131. That this decrease is less than for the unmodified rosin indicates that little, if any, of the rosin carboxyl group is esterified. After heating, the methylolated rosin still retained enough hydroxyl groups to undergo interesterification lvith linseed oil-when heated with an equal weight of oil a t 280' C. for 4 hours, she acid number decreased to 45.
Discussion
4.0 hr.
Color
240 200 157 168 140 115
122b llgb 14Qb 147 138 112
M K
127 128 98 117 112
107 105 92 110 107
I K
KI H G I I G-
Because methylolated rosin decreased only 15 units in acid number when heated for 3 hours a t 27.5' C., most of the decrease in acid number for the reactions discussed here probably resulted from esterification. Also, the acid condensates are probably esters of fatty acids. A reaction time of 3 to 4 hours seemed optimum for good color grade and minimum decarboxylation of rosin. Esterification for monobasic acids having up to 10 carbon atoms proceeded readily a t 225' to 280' C., and was practically complete in 4 hours as indicated by the drop in acid number of the mixture (Table I). As expected, the rate was slightly less as chain length of the esterifying acid increased. -4cetic
METHYLOLATED R O S I N anhydride reduced the reaction time by about 40%. The 'color grades in Tables I and 11 are those after 4 hours of reaction. At 2 to 3 hours, when reactions were essentially complete, the products were about two grades paler. The methylolated rosin showed a consistent decrease in acid number and a corresponding increase in viscosity on reaction with linseed oil (Table 11). Although the rosin carboxyl group in methylolated rosin does not esterify directly with the methylol groups, it does seem to facilitate the interesterification of linseed oil. The hydroxyl groups formed by the reaction of formaldehyde and rosin evidently cause an alcoholysis of linseed oil. The mono- and diglycerides thus formed may then react with the rosin carboxyl group; A little less than one half of the rosin carboxyl groups were esterified in 2 hours a t 280' C. The acid number drop after the first 2 hours was very slight. Reactions of linseed oil and tung oil in 12.5-gal. oil lengths (12.5 gallons of oil per 100 pounds of resin) when heated with methylolated rosin were compared with a control unmethylolated rosin reaction (Table 111). Pure tung oil will normally gel at 282' C. after 12 minutes. The reaction mixture showed no tendency to gel a t 295' to 300' C. for 0.5 hour and gave an excellent varnish film which dried hard in 3 hours. This varnish was slightly superior to the linseed counterpart varnish. Data from a 25-gal. linseed oil reaction, included in Table 11, showed a reaction rate equal to that of the 12.5-gal. runs. The final products have only slight odor of oil and are readily soluble in hydrocarbons. Since the more common esterification catalysts tend to darken resin products, the choice of catalysts for this work was somewhat limited (Table 11). Zinc oxide and magnesium hydroxide a t 1.0% concentration, forming resinates, were effective during first 2 hours reaction. Acetic acid either as free acid or as an exchange intermediate from the methyld a t e d rosin-acetate condensate was effective in promoting reaction between linseed oil and methylolated rosin. The use of abietic acid (acid No. 185; [ a ]= ~ -90') in lieu of rosin for this reaction gave no significant difference other than a paler product. Reactions using - linseed oil without catalysts were allowed to proceed at 280" C. for 3 hours and then held a t 290' C. for an additional hour (Figure 1). Because of interesterification, the products from the methylolated rosinlinseed runs showed an appreciably greater increase in viscosity.
Figure 3. rosin
This pilot plant kettle was used for esterification of methylolated
Table II.
lnteresterification of Methylolated Rosin with Drying Oil"
(280' C.; rosin-drying oil-paraformaldehyde ratio, 100:94:20) Catalyst or Exchange Intermediate
0.0 hr.
None, controlb Nonec None Acetic anhydrided Acetic acidd Control 1.0% ZnO ZnO, 0.1% ZnO, 1.0% Mg(OHh 1.0% Sn( shavings), 0.5% Ca(OHh 1.0% Adipic acid, 10% Nonee
89 96 84 58 82 80 90 86 81 84 85 170 59
Acid No. 1.0 hr. 2.0 hr.
4.0 hr.
Color Grade
Linseed Oil
+
86 58 56 49 57 68 54 51 52 68 60 112 47
85 54 47 34 40 66 51 46 42 55 52 90 34
82.5 46 44 32 38 66 43 35 38 49 48 81 26
M K-
I K I K K1I
H I I M-
Tung Oil
None 92 55 46 38 I Procedure 2. 100 g. rosin and 94 g. linseed oil; no formaldehyde or catalyst. Abietic acid used in lieu of rosin was methylolated. Rosin, formaldehyde, and acetic anhydride or acid reacted before addition of linseed oil. * Increased linseed oil, t o 188 parts or 25-gal. length varnish.
VOL. 50, NO. 8
AUGUST 1958
1129
appreciably less hardness at the end of 100 hours than their counterpart varnishes from methylolated rosin. The water resistance data presented in Table I V show the superiority of varnishes from methylolated rosin-drying oil over the control varnishes. Immersion of panels in distilled water a t 25" 2" C. caused the control films to whiten in about '/z the time of first white of varnishes from methylolated rosin. The latter varnishes appeared less white and recovered about twice as rapidly as control films after 36 hours' immersion. Resistance to boiling water showed even more significant difference in recovery time of the methylolated varnishes (0.5 to 0.6 hour) over control (2.0 to 3.0 hours). Methylolated rosinlinseed oil-adipic acid varnish showed excellent drying rate, hardness, and water resistance properties which compare favorably with the tung oil varnishes.
Varnishes prepared according to procedure 2, were diluted with mineral spirits to a viscosity of D. Driers in the form of resinates were added, and the resulting varnishes had a metal content of 1.0% zinc, 0.5% lead, and 0.05% cobalt, based on weight of drying oil used. Varnishes of linseed and tung oil acids were also prepared. Control varnishes of unmethylolated ester gum (rosin-glycerol ester) reacted with linseed oil, 12.5- and 25-gal. lengths, were prepared to compare their properties with those products from methylolated rosin. All of the varnishes in Tables I11 and I V were formulated to be equal in viscosity and driers, while solvent content deviated less than 10% depending on viscosity of original material. Samples of films were made in duplicate by dipping clean glass plates, 3l/4 X 4 inches, into the varnish, withdrawing slowly in 15 seconds, and allowing to drain set a t a 60" angle in a dustfree cabinet. The humidity during the drying ranged from 50 to 60% and temperature 25" rfr: 2" C. Table I11 shows that in general the control varnish films were considerably slower in both set to touch and drying time during a 24-hour period and showed
(1) Arundale, E., Mikeska, L. A., Chem. Revs. 51, 505 (1952). (2) Bain, J. P. (to The Glidden Co.), U. S. Patent 2,374,657 (May 1, 1945).
+
25
0.6
LO = linseed oil; T O a
3
4
14
..
24
28
42
oil Ester gum-linseed oil; no methylolation. Prepared from methylolated rosin, procedure 2. Prepared from methylolated rosin, procedure 1. = tung
36 Hours
Oil
Cold Water First Time t o Gal. white, clear, length hr. hr.
1 Hour
At 36 Hr. Time to Color
clear
Boiling Water Time to Condition, clear, 1 hr. hr. Med. white 0.45 Dense white 2.OC Med. white 0.60 Dense white 3.0 Med. white 0.4 Slight white 0.3
0.3 Linseeda 12.5 6 0.1 Med. white Linseedb 12.5 1.1 0.3 Dense white 0.5 Slight white 0.45 Linseed" 25 8 0.2 Linseed* 25 2.5 1.0 Med. white 1.5 20 0.6 LinseedaTd 12.5 Slight white 0.3 25 24 0.2 Slight white 0.2 Tung" a Product of reaction with methylolated rosin. Product of reaction with unmethylolated ester gum. Films after drying were slightly checked, dull, and peeled at edges of plate. Contained 10% adipic acid allowed t o react in 12.5-gal. linseed-rosin run.
1 130
INDUSTRIAL AND ENGINEERING CHEMISTRY
CORRECTION Triethanolamine Borate, Epoxy Resin Catalyst Choice Based on Reaction Mechanisms I n the article "Triethanolamine Borate, Epoxy Resin Catalyst Choice Based on Reaction Mechanisms," by S. H. Langer and I. N. Elbling [IND. ENG. CHEM. 49, 1113 (1937)], the following reference corrections should be made in the text: I n column 1, paragraph 3, last line reference should be ( 3 ) .
Table IV. Water Resistance of Varnish Films Compared (Methylolated and unmethylolated resin drying oil) ~
.
RECEIVED for review August 29, 1957 ACCEPTEDFebruary 26, 1958
literature Cited
Table 111. Comparison of Varnish Film Hardness (From glycerol esters of methylolated rosin-drying oil varnishes and ester gum-linseed oil varnishes) Time Set to Sward Hardness Type Gal. Touch, Hr. 2 hr. 4 hr. 8 hr. 18 hr. 24 hr. 100 hr. 9 16 20 32 1 4 Control, LOa 12.5 1.2 38 60 3 6 12 30 Lob 12.5 0.65 29 44 2 6 12 22 LO (acids)c 12.5 0.9 32 52 2 7 14 24 0.6 LO adipicC 12.5 15 30 32 44 4 8 0.5 TO acidsC 12.5 18 28 0 3 8 14 Control, LO" 25 1.5 26 34 0 4 12 L Ob 25 1.1 TOb
( 3 ) Bried, E. A. (to Hercules Powder Co.), Ibid., 2,383,289 (Aug. 21, 1945). (4) Gayer, F. H., Ibid., 2,744,889 (May 8, 1936). (5) Low, F. S., Ibid., 1,243,312 (Oct. 16, 1917). (6) McCutcheon, J. W., Organic Syntheses, collective vol. 111, p. 531, procedure A, Wiley, New York, 1955. (7) Palkin, S., Harris, T. H., J.Am. Chem. Soc. 56, 1935 (1934). (8) Prins, H. J., Chem. Weekblad 14, 932 (1917). (9) Royals, E. E., Green, J. L., Preprint Booklet, p. 161, Div. of Paint, Plastics, and Printing Ink Chemistry, 131st Meeting, ACS, Miami, Fla., April 1957. (10) St. Clair, W. E., thesis, Tulane University, 1949. (11) Stinson, J. S., Lawrence, R. V., IND.ENG.CHEM.46, 784 (1954).
In column 2. references in the last line of the paragraph should be (4>77, 72, 75).
O n page 1114, column 3, paragraph 3, reference in line 4 should be (5).
