CETYLENIC C G.L. FOSTER, B. C. H. KUCERA Dowell Division,
MANY
of the derivatives of propargyl alcohol are excellent corrosion inhibitors for acid solutions. A definite correlation exists between the relative inhibiting effectiveness of these derivatives and the nature and position of the various substituents. As oil wells are drilled deeper, and higher temperatures are encountered, inhibitors to prevent corrosion of oil well casing and tubing during acidizing have become more important. Recently, it was discovered that acetylenic compounds are effective inhibitors. I n this study, propargyl alcohol was selected as a standard acetylenic inhibitor, its structure was altered systematically, and the resulting compounds were evaluated as acid inhibitors.
Experimental Corrosion rates were determined on AISI Type 1020 mild steel coupons, inch. cut to a size of P / 4 X 1 X The coupons were pickled in lo?,’, hydrochloric acid for 10 minutes, then cleaned by scrubbing with soap and a toothbrush, rinsing with water, dipping in dilute sodium carbonate solution, and rinsing with water, and dried by rinsing with acetone. They were then weighed on an analytical balance and placed in 150 d.of test solution (acid containing
0.4% of various test inhibitors) preheated to the test temperatures. After a 16-hour exposure, the coupons were removed from the test solutions and the cleaning process was repeated. The coupons were then reweighed and corrosion rates calculated from the formula: Corrosion rate (Ib./sq. ft./day) = 49.15 X weight loss (g.) orginal weight (g.) X S. F. (sq. cm./g.) X time (hr.) where 49.15 = conversion factor, g./sq. cm./hr. to lb./sq. ft./day, and S. F. = strip factor = average ratio of coupon surface area (sq. cm.) to weight (grams) = 0.958 f 0.004 for AISI Type 1020 steel of the specified dimensions. (Conversion factor, lb./sq. ft./day to mg./ sq. dm./day = 48,800.) Corrosion tests were run in various concentrations of hydrochloric acid containing propargyl alcohol or one of the modified derivatives under test. I n selecting these compounds for study, each reactive site in the propargyl alcohol molecule-the methine hydrogen, the triple bond, the a-hydrogens, the hydroxyl group, and the alcoholic hydrogen -was systematically substituted. All compounds tested were purified by distillation or recrystallization. T h e acid corrosion rates at several temperatures and acid concentrations were determined
using each derivative. Effectiveness a t elevated temperature is the best criterion for inhibitor evaluation.
The Theory The extensive work in the field of corrosion inhibition has produced many theories concerning the mechanism of inhibitor action ( 2 , 5, 7). I t is generally agreed that inhibitors fall into two general types, anodic and cathodic. Anodic inhibitors function by sharing electrons with anodic sites at the metal surface, forming a dative bond. Cathodic inhibitors function by forming a protective film on the metal surface by attraction of the inhibitor to cathodic areas through electrostatic attraction. I t is suggested that acetylenic compounds function as anodic inhibitors by the sharing of a electrons with anodic sites on the metal surface. It is further suggested that the availability of these a electrons is influenced by substituent groups. Acetylenic compounds form n complexes with metal ions (7, 3, 6, 10). Hydrochloride salts of alkynes have been prepared ( 4 ) and bear a resemblance to amine hydrochlorides. The effectiveness of an anodic inhibitor should be related to the strength of the inhibitor-metal bond. No quantitative measurements of this linkage were
Theory and Practice
This article describes the systematic substitution of each reactive site in the propargyl alcohol molecule-the methine hydrogen, the triple bond, the a-hydrogens, the hydroxyl group, and the alcoholic hydrogen-and how this substitution affects corrosion inhibition. Theory indicates that the triple bond is the focal point of this inhibitory action, and the experimental results confirm it. The results outlined in this article point the way toward the development of more effective corrosion inhibitors. VOL. 51, NO. 7
JULY 1959
825
made. However, from a study of the test results such a relationship can be inferred. Furthermore, classical theories of the inductive effects of various substituent groups (9) provide a method for predicting effectiveness within a given group of compounds. The inductive effect of substituents tends to influence the availability of .rr electrons on the triple bond, thus modifying the effectiveness of the inhibitor. Relative acid corrosion rates observed using these various compounds are shown in Table I.
Table I. Effect of Substitution on the Acid-Inhibiting Properties of Propargyl Alcohol With one exception none of these compounds is an good an inhibitor as propargyl alcohol
7
@ p H/ @ ? H-CEC-C-0-H
u\
The Results Replacement of Methine Hydrogen. Compounds 3 to 7 in Table I show the result of replacing the methine hydrogen. None of these compounds is as good an inhibitor as propargyl alcohol. Electronegative substituents tend to decrease the over-all polarization by operating against the hydroxyl group; hence the corrosion rate increases. Although the methine hydrogen would appear to be an essential structural feature, comparison with compound 32 shows that this is not the case. Reduction of Triple Bond. Compounds 8 and 9 show the effect of saturating the acetylenic bond by hydrogenation. The more saturated compounds are less effective inhibitors. Table I1 gives corrosion rates when a small percentage of mercuric chloride salt is added to the acid. Mercury salts catalyze the hydration of triple bonds in acid media. As the concentration of mercury increases, so does the corrosion rate, supporting the previous observation that the triple bond is essential for inhibition. Comparison of the effect of a mercury salt on an organic inhibitor that does not contain unsaturated linkages is included to show that only a small loss of inhibition is observed in this case.
Corrosion R a t e , Lb./Sq. Ft../Day 175O F. 200' F. 10% HC1 15% HC1 15% HCl 150' F.
Compound 1.
Blank (no indicator)
>1
>1
2. E fi=C-,cH20H
0.003
0.01
>1 0.05
I. Replacement of Methine Hydrogen 3.
Cl-C3C-CHzOH
0.003
0.07
...
>1
I-C=C-CH~OH 5. HO-CH2-C~C-C~C-CH2-oH
0.02
o.ol
0.14
>1
6. Cl-CHn-CSC-CHz-OH 7* Ho-cH~-c~C-cH~-oH
0.01
0.14
>1
0.07
0.20
>1
4.
11. Reduction of Triple Bond 0.27 >1
8. HzC=CH-CHr--OH
9.
Hac-CHz-CHz-OH
>I
...
... ...
...
0.003
0.07
0.70
0.002
0.003
>1
0.004
0.007
>1
0.003
0.04
>I
0.003
0.9
111. Replacement of a-Hydrogens H
/
10. H-CSC-C-OH
\ CHa 11. H-C=C-C-OH H3C
,."
x3 H
12. H-C=C-C-OH
/ I
H3c-0-cHH
Table II.
Effect of Triple Bond Hydrationa
Corrosion rate increases with mercury concentration Corrosion Rate,
74
%
Concn. HgClz
CH3
/
14. HZSC-C-C-OH
\
Lb./Sq.
Ft./Day Propargyl alcohol 0.4 0 0.01 0.5 0.70 1.0 >1 AIOOb 0.6 0 0.01 0.5 0.04 1.0 0.1 Tests run in 10% "21, 16 hours, 175' F. Mixture of organic compounds used commercially as a hydrochloric acid corrosion inhibitor. Inhibitor
/
13. H-CSC-C-OH \ CHz-CHa-CH~-CHa
...
CHr-CHpCHI-CHs
CH3 /
15. H-CSC-C-OH
0.003
>1
0.04
>I
\
CH3
CHI
16.
/ H-c~C-c-oH \
...
CHz-CHs
CH3
17. H-C=C-C-OH
Replacement of a-Hydrogens. Compounds 10 to 13 show the effect of replacing one a-hydrogen atom with an alkyl group. Electropositive substituents
826
INDUSTRIAL AND ENGINEERING CHEMISTRY
/ \
0.15
...
ACETY L E N l C CORROSION I N H I B I T O R S Table 1.
Effect of Substitution on the Acid-Inhibiting Properties of Propargyl Alcohol (Continued) IV. Replacement of Hydroxyl Group
18. H-CEC-CHpSH
...
19. H-C=C-CHz-NH 20. 21. 22. 23.
V.
25.
>1
0.19
...
H-CSC-CHz-N(CHs)z H-CEC-CHaCl H-C=C-CHpN[CH(CHs)sJ2 H-CEC-CHz-NHz
24. H-C=C-CHa-O
...
0.001
e..
... ... ...
0.25 >1
0.1 0.5 >1
e..
... ...
Replacement of Alcoholic Hydrogen CSC-H
8
H-C%C-CHz-O-CHz-CH-CHz
0.0015
0.02
0.17
0 02
0.02
0.17
0.004
0.03
>1
0.004
0602
>I
\ / 0
26. H--C~C-CHa-O-C-C&
/I
0
28.
0 H-C~C-CHP-O-C II - C H S - O ~
cis 0.6
...
>1
29. H-C=C-CHZ-O-SO2 >I
... ...
e..
0
//
30.
e..
C
/-\
H
CHs
VI. Effect of Chain Length 3 1.
H-C~C-CH~-CHaOH
0.01
0.05
>I
I and 111. Replacement of Methine Hydrogen and or-Hydrogens CHI
/
32. I-CZC-C-OH
...
0.002
\
0.004
CHs CHs
/
33. I-CgC-C-OH
\
\ HO-C-C=C-C=C-C-OH / Hac
CHI 35.
>1
*..
0.008
>I
...
CHzCHs
Hac
34.
0.006
\/
HO-C-C=C-C-OH CHa-CHI 111 and IV.
CHa
/ \
CHa
/CHa \
0.5
I . .
>I
CHeCHs
Replacement of a-Hydrogens and Alcoholic Hydrogen
36. H-CSC-C-O-
0.006
0.4
0.01
0.76
e..
\ ‘0 CHa
/ CDHl8
>1
in the a position counterbalance the attraction of the hydroxyl group by supplying electrons to the a-carbon. The electronegative pull of the hydroxyl group is partially neutralized by alkyl groups a to the triple bond, and the corrosion rate increases accordingly. When two alkyl groups are introduced in place of the a-hydrogen atoms, the corrosion rate is further increased, as would be predicted (compounds 14 to 17). Corrosion rates, using compounds 14, 15, and 17, do not follow in sequence according to the size of substituent. Both the methyl propyl alcohol (14) and dimethyl alcohol (15) are better inhibitors than the ethyl methyl derivative (17). This indicates that steric factors do not play a n important role in this series. Replacement of Hydroxyl Group. Compounds 18 to 23 are poor inhibitors, for the most part. For this reason, the various classes of compounds were not investigated in detail, as the results would not have much meaning. Propargylamine, on the basis of polarization, should be a superior inhibitor because it possesses two centers which could attach to the metal surface-the nitrogen atom and the triple bond-and polarization should be enhanced if the nitrogen becomes protonated in the acid solution. This apparent anomaly may be due to the fact that propargylamine hydrochloride is a n unstable compound (8) and apparently decomposes readily in hot acid solution. Replacement of Alcoholic Hydrogen. Compounds 24 to 30 show the effect of replacement of the alcoholic hydrogen atom. Compounds 24 to 27 are formed from groups not removable by acid hydrolysis, except under strenuous conditions. Compounds 28 to 30 are subject to rapid acid hydrolysis. Effect of Chain Length. Increasing the distance of the hydroxyl group from the triple bond decreased inhibitor effectiveness, as shown by compound 31. This would be predictable on the basis that the electronegative hydroxyl group is removed further from the triple bond. Replacement of Methine Hydrogen and a-Hydrogen. Compounds 32 to 35 show the effect of replacing the ahydrogen and the methine hydrogen simultaneously. I t was anticipated that changing more than one substituent a t a time might result in changes in corrosion rates which would be difficult to explain. For example, iodopentynol (compound 32) is a better inhibitor than propargyl alcohol. This would indicate that the electropositive methyl groups neutralize the effect of the hydroxyl group, and that the triple bond is polarized in the direction of the iodine atom. A comparison of several iodo- and chloroacetylenic alcohols (Table 111) illustrates VOL. 51, NO. 7
JULY 1959
827
Table 1.
Effect of Substitution on the Acid-Inhibiting Properties of Propargyl Alcohol (Continued)
‘, l H i
A
CH3 38. H--C=C-C-O--
0.005
...
>1
‘0’
CH3 CHa A H 39.
...
0.006
H-CzC-d-0
A 40.
41.
H-C=C-C-O
,
‘0’
CzHs CH3
n
H-&C-C-0
0.3
>1
...
0.8
>1
...
C~H@(iso)
Table 111.
Sufficient Polarization in Either Direction Gives Good Corrosion Rates Xet
Inhibitor
Polarization
I t CESSC-C + OH
Corrosion Rate, Lb./Sq. Ft./Day, 150° F., 10% HC1 0.002
1
0.02
>1
0.5
>1
0.9
>I
Inhibitor
I
OH
I
0.20
OH
I-C=C-I CI-CHz-CSC-CHz-Cl CH3 CH3 I I CH~-CH-C-C=C-C-CH~-CH~ II II OH OH HO&-WC-COzH
828
0.07
INDUSTRIAL AND ENGINEERING CHEMISTRY
the principle that sufficient polarization in either direction gives good corrosion rates. Propargyl alcohol is polarized in the direction of the hydroxyl group, whereas chloropropargyl alcohol is polarized in the opposite direction. The direction and length of the arrows in Table I11 indicate the direction and net polarization as derived from corrosion rates. Replacement of a-Hydrogen and Alcoholic Hydrogen. Replacing both of the a-hydrogen atoms and the alcoholic hydrogen produced poor inhibitors (compounds 36 to 41). None of these compounds is as good as propargyl alcohol. All are ketals formed by reaction of the corresponding alcohols with dihydropyran, and are easily hydrolyzed in acid solution. Corrosion rates of the ketals, as would be expected, parallel those of the parent alcohols. Effect of Symmetry. Corrosion rates for compounds with widely varied structures are given in Table IV. The one salient feature of all is their symmetry about the triple bond. These compounds, in keeping with their balanced polarization, are all poor inhibitors.
Conclusions T h e triple bond is the focal point of the inhibitive effect of acetylenic derivatives in acid solutions. Certain substituent groups in the molecule affect the donor capacity of the electrons in the triple bond and the corresponding ability of the molecule to inhibit. Acknowledgment The authors express their thanks to Roger F. Monroe and Fred J. Lowes of the Midland Division, The Dow Chemical Co., for supplying many of the compounds used in this study. Literuture Cited (1) Chatt, J., Row, G. A., Williams, A. A,, Proc. Chem. Sac. 1957, p. 208. (2) Ch’iao, S.-J., Mann, C. A,, IND.ENG. CHEM.39, 910 (1947). (3) Clarkson, R., Jones, E. R.H., Wailes, P. C., Whiting, M. C., J. Am. Chem. Soc. 78, 6206 (1956). (4) Cook, D., Hupien, Y., Schneider, W. G., Can. J. Chem. 34, 957 (1957). (5) Gatos, H. C., Corroszon 12, 235 (1956). (6) Greenfield, H., others, J. Am. Chem. Soc. 78, 120 (1956). (7) Hackerman, N., Makrides, A. C., IND. ENC.CHEM.46, 523 (1954). (8! Heilbron, I. M., Bunbury, H. M., ’Dictionary of Organic Compounds,” 2nd ed., vol. IV, p. 234, Oxford Univ. Press, New York, 1953. (9) Remick, A. E., “Electronic Interpretations of Organic Chemistry,” Chap. V, 2nd ed., Wiley, New York, 1949. (10) Reppe, W., Vetter, H., Ann. 582, 133 (1953). RECEIVED for review May 8, 1958 ACCEPTED March 23, 1959 Organic Division, 13th Southwrst Regional Meeting, ACS, Tulsa, Okla., December 6 , 1957.
