Alkaline hydrolysis of alkylated acidic groups on carbon black

Carbon,1976, Vol.14,pp.247-251.PergamonPress. Printed inGreatBritain

ALKALINE HYDROLYSIS OF ALKYLATED ACIDIC GROUPS ON CARBON BLACK YOSHIMIMATSUMURA National Institute of Industrial Health, 6-21-1,Nagao, Tama-ku, Kawasaki-213,Japan

and SHIGFJ

HAGIWARAand HIROSHI TAKAHASHI Institute of Industrial Science, University of Tokyo, 22-1, Roppongi 7-chome, Minato-ku, Tokyo-106, Japan (Received 8 May 1976)

Abstract-Potentiometric pa-stat titration was performed on alkylated carbon black dispersed in aqueous solution at pH 9.0, 10.0and 11.0and alkaline hydrolysis rate constant of the alkylated functional groups on the carbon black was obtained therefrom. Carbon black treated with C,-C, n-alcohols in vapor or liquid phase was used in this experiment. Hydrolysis proceeded more rapidly for carbon black treated with lower alcohols. For each alkylated carbon black, the hydrolysis rate constant decreased with time and, after the hydrolysis rate diminished, a hydrolysis resistant fraction of alkylated groups remained. For example, the hydrolysis rate constants at 25°C were 24.33, 17.50and 4.501. mol? . sect’ at 15min and 6.00,6.00 and 3.671. mol-’ . see-’ at 45 min after the start of hydrolysis at pH 9.0 for carbon black treated with C,, C, and Cq alcohols respectively.

1. INTRODUCTION The alkylation of oxygenated functional groups on industrial powdered materials such as silica has been

alcohol remaining on the carbon black was extracted with acetone and the carbon black was dried in vacuum. The alkylation of the acidic groups on carbon black was determined by titration curve measurements as described in the previous paper[6]. The titration curve for nbutylated Peerless-155 is shown in Fig. 1 as an example, with the curves for the untreated Peerless-155 and a blank solution. The decrease of the acid and the change of the surface area of the carbon black due to the alkylation are summarized in Table 1. The degree of alkylation presented in Table 1 was the ratio of the amount of acid in the treated carbon black to that in the original one, both of

performed to change the hydrophilic surface into a hydrophobic one and to extend their industrial applicability [l, 21, but there are few examples of the alkylation of carbon black for the purpose of changing its properties. Hofmann and Ohlerich131 and other investigators [4,5] have methylated functional groups on carbon black with diazomethane in order to identify the surface groups present. They suggest that the accessibility of the group to methylation and the stability of the resultant methylated groups towards hydrolysis were dependent upon the type, of surface group, i.e. carboxylic acid, phenolic hydroxide, enol or lactone. In this study, we prepared alkylated carbon black by the treatment of furnace black with C& n-alcohols in the vapor or liquid phase. In order to examine the chemical stability of the produced alkylated groups, automatic potentiometric pH-stat titration was performed for the suspensions of the carbon black at pH 9.0,lO.O and 11.Ofor 1 hr and from the pa-stat titration curves, alkaline hydrolysis rate constant of the alkylated carbon black was derived. 2. FXPFXIMENTAL Colour furnace black, Peerless-155 from Columbian Carbon Co., was treated with n-alcohol homologues from C& in either the vapor or liquid phase. For vapor phase alkylation, carbon black was put in a stainless steel mesh basket hung in a glass vacuum vessel, evacuated at 120°C under 10m5 torr for 24 hr and alcohol vapor was introduced into the vessel where it was in contact with carbon black at a temperature a few degrees higher than the boiling point for 5hr. For liquid phase treatment, carbon black was pre-evacuated at 10e5torr and at 120°C for 24hr, sealed in a glass ampoule and then brought into contact with alcohol in a flask provided with a reflux condenser, and refluxed for 24hr. After the treatments, unreacted

12.0.

1

Blank solution n-Butylated

Peerless-155

Peerless-155

0.0

u.

I

u.z

0.3

Amount

0.4 of

added

0.5

0.6

alkali,

0.7 m

eqlg

Fig. 1. Titration curves of Peerless-155 original and n-butylated in the vapor phase and of a blank solution.

247

248

Y. MATSUMIJRA et al.

Table 1. The propertiesof carbon black treated with n-alcohols in vapor and liquid phases Kinds of alcohol

Specific

Surface

Degrees of

used for carbon

surface area

acidity a)

alkylation b)

black treatment

(m2/g,

0.ies/m*)

Original Ethanol

(vapor)

n-Propanol

129.7

0.801

0.0

126.6

0.200

75.0 77.4

122.5

0.181

n-Butanol

(vapor)

121.5

0.200

75.0

n-Hexanol

(vapor)

124.4

0.154

80.8

n-Octanol Methanol Ethanol

(vapor)

(%)

(vapor)

113.2

0.062

92.3

(liquid)

112.8

0.461

42.5

(liquid)

n-Butanol

(liquid)

126.6

0.487

39.3

113.1

0.224

72.1

a) : Surface acidity is expressed by the amount of acid determined by neutralization

of specimen suspension up to pIi 7.0.

b) : Degrees of alkylation

are presented by the decrease of surface

acidity in percentages.

which were determined from the amounts of alkali added to the specimen suspensions up to pH 7.0 in the titration curves. The hydrolysis was observed by a pa-stat titration method using Radiometer Titrator 11 combined with a pH meter PHM 26, a glass-calomel combined electrode, autoburette and a recorder. Alkylated carbon black (0.2 g) was dispersed in 1.0 M sodium chloride solution (15 ml) kept at a constant temperature of 25 + O.l”C. The electrode and a teflon tube delivering a sodium hydroxide solution from the reservoir were inserted into the bottle containing the suspension, and the bottle neck was tightly sealed with putty. The pH of the suspension was rapidly adjusted to 9.0, 10.0 or. 11.0 within 10 min by adding sodium hydroxide solution of 0.1 M, and was then kept at constant pH by the automatic; incremental addition of alkaline solution. The added amount of alkali was recorded in the course of time, from which hydrolysis rate constant was derived as follows according to eqn (1). Alkaline hydrolysis of esters is second order, depending on the concentrations of ester and alkali. In pa-stat solution, the concentration of alkali is constant and consequently the hydrolysis rate of the ester is expressed by the equation, $=k(A

-x)B

(1)

where x is the concentration of hydrolyzed ester at time t, t is the elapsed time from the start of hydrolysis, k is hydrolysis rate constant, A is the initial concentration of ester and B is the concentration of alkali. Thus, the hydrolysis rate constant k is derived as (the differential coefficient of the pa-stat titration curve) divided by both of (the amount of residual ester) and (the concentration of alkali). Here, x is equal to the amount of added alkali to the suspension at time t, because the acid liberated from ester by hydrolysis is neutralized by equimolar alkali in pa-stat. The amount of residual ester at time t for the alkylated carbon black is obtained as the difference of the

amounts of added alkali to neutralize original carbon black and the alkylated one at time t at the same pH of 9.0, 10.0 or 11.0 respectively. 3.RESULTS AND DISCUSSION

The surface acidic groups on carbon black were alkylated with n-alcohols by vapor or liquid phase treatment to the extent from 39.3 to 92.3% as shown in Table 1. The higher homologues tend to give higher alkylation yields. This might be due to the higher temperature adopted for the treatment of alkylation and the larger molecular size of the alkyl groups which might cover more than one acidic group on carbon black surface. pH-stat titration curves of the alkylated carbon blacks and the hydrolysis rate constants derived from them showed that: (1) hydrolysis proceeds faster in the suspension at higher pH and for the carbon black alkylated with lower alcohols, (2) hydrolysis rate and hydrolysis rate constant for an alkylated carbon black were greatest initially and then decreased with time and that (3) hydrolysis rate constant of an alkylated carbon black at time t was greater for the hydrolysis at lower pH. pH-stat titration curves for n-butylated Peerless-155 at pH 9.&l 1.0 and the derived hydrolysis rate constants are shown in Figs. 2(a) and 2(b). The untreated Peerless-155 shows pH-stat titration curves with small inclinations which is considered to be attributed to the approach to acid-base equilibrium and not to the hydrolysis of any ester or lactone groups in the sample [6]. The pH-stat titration curves for the alkylated specimens were corrected for the curves for the untreated sample to the extents depending on the amount of acidic groups remaining on the alkylated specimens, because some acidic groups remained on carbon black after the alkylating treatments. The larger hydrolysis rate at higher pH of the suspension is common with organic esters because of the higher concentration of alkali. The variations of the hydrolysis rate constant with time and with the pH of the

249

Alkaline hydrolysis of alkylated acidic groups on carbon black 0.7

(A) Original Peerless-15E

t

_____ _______

1

," 0.6 E

Amounts of alkylated groups remaining on the specimens

come to predominate at an earlier stage in the former than in the latter. Hydrolysis at pH 9.0 of the carbon black alkylated with C2, C, and C., alcohols in the vapor phase, and the corresponding hydrolysis rate constants, are presented in Figs. 3(a) and 3(b). n-Hexylated and n-octylated carbon blacks showed no observable hydrolysis within 1 hr at pH 11.O.These samples also showed so little wettability with aqueous medium that the sample could be suspended only by instant breaking of vacuum glass ampoules containing the sample in the medium followed by removal of the glass. The stability of the alkylated groups on these carbon blacks against hydrolysis could be partly due to the unwet~b~ity of the surface, as suggested by Iler for alkylated silica[l]. The progress of the hydrolyses for the alkylated carbon

(A) 0

10

20

30

40

50

60

Time,

min

Fig. 2(a). pH-stat titration curves at 25°C for n-butylated Peerless-155 prepared by vapor phase treatment. The specimen (0.2g) was suspended in 1.0M sodium chloride solution (15 ml) and hydrotyzed at pH 9.0,lO.Oand 11.0.

Original Peerless-155 '-_Ixf_____________' A~unts of alkylated groups remainin on the specimens

10

0

20

30

40

50

Time,

60

min

Fig. 3(a). pH-stattitrationcurves for e#yla~, ~-propylatedand n-butylatedPeerIess-155at pH 9.0 and 25°C.The specimens were

J 0

IO

20

30

I

I

40

50

Time,

I 6 min

Fig. 2(b). Hydrolysis rate constants derived from the hydrolysis progress presented as pH-stat titration curves in Fig. 2(a).

suspension are consistent with the general concept of alkaline hy~olysis of mixed esters with various hydrolysis rate constants. Carbon black treated with lower alcohols was more rapidly hydrolyzed at the start of the experiment than those treated with higher alcohols, but the hydrolysis rate decreased with time and in some cases became slower than that for the carbon black alkylated with the higher alcohols. This tendency could also be interpreted by the presence of various types of alkylated groups, each with different hydrolyzability on carbon black. For instance, labile groups in ethyfated carbon black would be more rapidly hydrolyzed than those in ~-propylated carbon black, and the less-labile groups

0

10

20

30

40

50 Time,

60 min

Fii. 3(b). Hydrolysis rate constants derived from the hydrolysis progress presented as pa-stat titration curves in Fig. 3(a).

Y. MATSUMURA et al.

250

blacks are tabulated in Table 2 and the hydrolysis rate constants derived therefrom are summarized in Table 3. The hydrolysis rate constants for the carbon blacks alkylated with C& alcohols range from 40.50 to 4.83 1. mol-’ *set-’ at 10 min from the start of hydrolysis at pH 9.0; these are far greater than the reported saponification rate constants of acetates and benzoates. For instance, the saponification rate constants at 25°C for ethyl, n-propyl and n-butyl acetates are 0.110,0.095 and 0.0911. mol-’ . set-’ respectively[7]; those for methyl, ethyl, II-propyl and n -butyl benzoate are 0.00902,0.00289,

0.00193 and 0.001671. mol-’ *set-’ respectively[8]. The rapid hydrolysis of the alkylated groups on carbon black could be related to the structure of both of the surface functional groups and the microcrystalline micelles in the bulk, and the surface density of the alkylated groups. It might be presumed that the alkylated groups on the carbon black surface would be more prone to hydrolysis than organic esters due to the steric strain and electronic configurational interference from adjacent groups. The larger hydrolysis rates might be also attributed to the fact that the acidic groups covered by adjacent esterified

Table 2. Time-course of pa-stat titration of original and alkylated carbon black suspensions at pH 9.0,lO.Oand 11.0 at 25°C Kinds used

of alcohol

pH for

for carbon

black

treatment

titration

Original

Ethanol

(vapor)

n-Propanol

n-Butanol

Amounts

pH-stat

(vapor)

(vapor)

of titrated

Time

from

alkali

the start

1O

20

30

(m eq/g-carbon)

of hydrolysis

40

(rain)

50

60

9.0

0.124

0.130

0.132

0.134

0.135

0.136

10.0

0.188

0.196

0.202

0.206

0.209

0.210

11.0

0.442

0.459

0.470

0.476

0.482

0.487

9.0

0.066

0.079

0.087

0.091

0.093

0.095

10.0

0.120

0.141

0.155

0.165

0.170

0.174

9.0

0.059

0.066

0.071

0.075

0.077

0.079

10.0

0.106

0.115

0.120

0.126

0.129

0.133

9.0

0.031

0.034

0.037

0.040

0.043

0.045

10.0

0.103

0.109

0.114

0.120

0.122

0.123

11.0

0.299

0.322

0.335

0.344

0.352

0.359

n-Hexanol

(vapor)

11.0

0.225

0.230

0.230

0.230

0.230

0.230

n-Octanol

(vapor)

11.0

0.267

0.271

0.271

0.271

0.271

0.271

(liquid)

9.0

0.092

0.095

0.096

0.096

0.096

0.096

10.0

0.130

0.137

0.139

0.139

0.139

0.139

9.0

0.092

0.095

0.096

0.096

0.096

0.096

10.0

0.130

0.137

0.139

0.139

0.139

0.139

9.0

0.043

0.053

0.062

0.069

0.073

0.078

10.0

0.081

0.095

0.103

0.110

0.118

0.127

11.0

0.306

0.324

0.362

0.372

0.380

0.386

Mathanol

Ethanol

(liquid)

n-Butanol

(liquid)

Table 3.

Hydrolysisrate

Kinds

of alcohol

used black

constants of alkylated carbon black at 25°Cin the time-course of alkaline hydrolysis

for carbon treatment

Ethanol

(vapor)

n-Propanol

n-Butanol

(vapor)

(vapor)

pH for

Hydrolysis

pH-stat

Time

titration

rate

constants

from the start 15

(liters.mol

of hydrolysis

30

45

9.0

24.33

9.83

6.00

10.0

4.92

2.37

0.98

9.0

17.50

8.00

6.00

10.0

1.68

1.03

0.77

9.0

4.50

3.83

3.67

10.0

1.42

0.77

0.37

11.0

0.18

0.095

0.072

n-Hexanol

(vapor)

11.0

0.00

0.00

n-Octanol

(vapor)

11.0

0.00

0.00

(liquid)

9.0

13.67

1.33

0.00

10.0

1.05

0.58

0.08

9.0

20.83

16.00

11.83

Methanol

Ethanol

n-Butanol

(liquid)

(liquid)

10.0

2.17

1.60

0.98

9.0

22.33

16.00

9.83

10.0

2.25

1.47

1.45

11.0

0.18

0.13

0.06

-1 -1 .sec 1 (min)

Alkaline hydrolysis of alkylated acidic groups on carbon black groups would become exposed to the medium at the same

time as the hydrolysis. These hydrolysis observations disclose the presence of various kinds of alkylated groups with different hydrolyzability on carbon black. In methylated carbon black, for instance, the hydrolysis rate was so rapid at the start that the precise determination of the rate was impossible. All the hydrolyzable groups on the methylated carbon black seemed to react within 20 min at pH 9.0 and 10.0, and then the rate decreased to zero. There remained unhydrolyzable groups in the amounts of 0.040 and 0.050 m equiv./g in the medium at pH 9.0 and 10.0 respectively. Based on the concept that carboxylic acid esters are hydrolyzable and ethers of phenolic hydroxides are unhydrolyzable [3], the unhydrolyzed fraction could be attributed to alkylated phenols. For carbon black alkylated with higher alcohols, hydrolysis progressed more slowly and the fractions of the hydrolyzable and unhydrolyzable groups could not be discerned after 1 hr. The amounts of alkylated groups remaining after 1 hr

251

were larger for the carbon blacks treated with higher alcohols as seen in Table 2. The carbon black treated with alcohols in the vapor phase were a little more hydrolysisresistent than those treated in the liquid phase. The higher temperatures for the treatments with higher alcohols and in the vapour phase could be the cause of the more hydrolysis-resistent properties. REFERENCES

1. R. K. Iler, The Colloid Chemistry ofSilicaand Silicates, p. 257. Cornell University Press, New York (1955). 2. K. Tsutsumi, H. Emori and H. Takahashi, Bu11.Chem. Sot. Jap. 48, 2613 (1975). 3. U. Hofmann and G. Ohlerich, Angew. Chem. 62, 16 (1950). 4. M. L. Studebaker, E. W. D. Huffman. A. C. Wolfe and L. G. Nabors, Ind. Engng Chem. 48, 162 (1956). 5. V. A. Garten, D. E. Weiss and J. B. Willis, Austral. J. Chem. 10, 295 (1957). 6. Y. Matsumura, S. Hagiwara and H. Takahashi, Carbon 14, 163 (1976). 7. D. G. Flom and P. J. Elving, Anal. Chem. 25, 541 (1953). 8. E. Tommila,Arm. Acad. Sci. Fennicae, Ser. A59(3),3 (1942).