SovietRxiv

Rate of Oxidation of Polyhydric Alcohols by Potassium Permanganate

B. V. Tronov and M. P. Sinyavin.
Submitted 1931 | SovietRxiv: ru-193101.07626 | Translated from Russian

Abstract Generated abstract

This study examines the oxidation rates of a series of polyhydric alcohols and sucrose by potassium permanganate in neutral and alkaline media. The reactions were followed by titrating residual oxidant at timed intervals under varied concentrations and temperatures, and apparent rate values were compared at equal stages of permanganate consumption because simple kinetic equations did not give constant values. The results indicate that oxidation generally accelerates with increasing number of hydroxyl groups, with marked increases from glycerol to higher polyols, while tertiary glycols such as pinacol react very slowly and stereoisomeric differences among hexitols appear small. Alkali greatly increases oxidation rates, often by tens or hundreds of times, although no simple relation was found between this acceleration and the intrinsic oxidizability of each alcohol.

Full Text

B. V. Tronov and M. P. Sinyavin.

Rate of Oxidation of Polyhydric Alcohols by Potassium Permanganate

In one of the preceding works*) on the oxidation of organic compounds, the action of \(KMnO_4\) on a large series of alcohols, chiefly monohydric ones, was studied. The rate of the reaction in neutral and partly in alkaline medium was measured. With polyhydric alcohols \((CH_2OH—CH_2OH,\ CH_2OH—CHOH—CH_2OH,\ CH_2OH—CHOH—CH_2OH,\) pinacol, erythritol, adonitol, mannitol) only a few experiments were carried out, and exclusively in neutral solution.

In the present work a larger number of alcohols has been considered; the reaction was studied not only in neutral, but also in alkaline medium, sometimes also at different temperatures and concentrations, which was especially necessary in view of the very great difference in oxidizability among certain compounds.

The following polyhydric alcohols were taken:

  1. \(CH_2OH . CH_2OH\).

  2. \(CH_2OH . CH . CHOH\).

  3. \((CH_3)_2COH . COH(CH_3)\).

  4. \(CH_2OH . CHOH . CH_2OH\).

  5. \(CH_2OH . CHOH . CHOH . CH_2OH\) (erythritol).

  6. \(C(CH_2OH)_4\).

\[ \begin{array}{cc} CHOH & CHOH \end{array} \]

  1. \(CH_2\) — \(CHOH\) (inositol).

\[ \begin{array}{cc} CHOH & CHOH \end{array} \]

  1. \(CH_2OH . CHOH . CHOH . CHOH . CHOH . CH_2OH\) (mannitol).

  2. \(CH_2OH . CHOH . CHOH . CHOH . CHOH . CH_2OH\) (sorbitol).

  3. \(CH_2OH . CHOH . CHOH . CHOH . CHOH . CH_2OH\) (dulcitol).

  4. Sucrose.

The substances investigated were distilled before the experiments (glycerin in vacuo) or recrystallized.

In the majority of experiments the concentration of each of the components (alcohol, \(KMnO_4\), and \(NaOH\), if the oxidation was conducted in alkaline solution) was \(0.03\) mole per liter. The temperature was from 16 to \(21^\circ\), or \(3^\circ\). The course of the reaction was followed by titrating the oxidizing agent remaining after definite intervals of time.

The oxidation products were not investigated.

*) V. V. Tronov, A. A. Lukashin, and I. I. Nalimov, Zh. R. Kh. O., 59, 1175—1197 (1927).

The results of the work are expressed in the following tables, where, for each experiment, the concentrations of all components, the temperature, the time intervals \((t)\) after which titration was carried out, the percentage of active oxygen remaining (the reduction of Mn during titration proceeded to the divalent state), the amount of oxidizing agent that had reacted (i.e., active oxygen proper), expressed in moles of \(\mathrm{KMnO_4}\) per liter \((X)\), the amount of oxidizing agent remaining in moles of \(\mathrm{KMnO_4}\) per liter \((a-x)\), and the rate constant, calculated from the equation for a bimolecular reaction:

\[ K=\frac{x}{t(a-x)a}. \]

For those experiments in which the concentrations of alcohol and \(\mathrm{KMnO_4}\) were the same; in the case of a large excess of one of the reacting compounds, the constants were calculated from the equation for a monomolecular reaction.

Experiments in a Neutral Medium

1. TRIMETHYLENE GLYCOL.

Temperature \(17\text{—}18^\circ\mathrm{C}\). Concentration of \(\mathrm{KMnO_4}\) and of the alcohol—0.03.

\(t\) \(x\) \(a-x\) \(K\) \(\mathrm{O_2}\%\)
0 0 0,029847 — 100
1 0,000127 0,029720 0,14316 99,57
10 0,000730 0,029117 0,08401 97,55
20 0,000794 0,029053 0,04579 97,34
130 0,002540 0,027307 0,02402 91,49
200 0,003366 0,026481 0,02129 88,72
260 0,004287 0,025560 0,02161 85,64
320 0,005052 0,024795 0,02133 83,08
365 0,005717 0,024130 0,02174 80,85
1320 0,012304 0,017543 0,01780 58,78
1560 0,013634 0,016213 0,01804 55,58
1740 0,014098 0,015749 0,01723 52,77
2730 0,011352 0,013495 0,01032 45,21

2. PINACON.

Temperature 18–19°C. Concentration of KMnO₄ and alcohol 0.03.

t x a-x K %%
0 0 0.030013 — 100
329 hours 0.000031 0.029682 0.0000017451 99.89
450 " 0.000126 0.029887 0.0000005084 99.58
616 " 0.000316 0.029697 0.0000005927 98.94

3. PENTAERYTHRITOL.

Temperature 21°C. Concentration of KMnO₄—0.03 m., alcohol—0.03.

t x a-x K %%
0 — 0.0301 — 100
3 0.00226 0.02784 0.8988 92.51
5 0.00897 0.02113 2.8206 70.02
7 0.01302 0.01708 3.6170 56.76
9 0.01637 0.01373 4.3988 45.64

4. MANNITOL.

Temperature 21°C. Concentration of KMnO₄, alcohol 0.05.

t x a-x K %%
0 0 0.029910 — 100
1 0.000388 0.029522 0.4394 98.72
5 0.001318 0.028592 0.3082 95.59
10 0.010642 0.019268 1.8465 64.43
15 0.011298 0.018612 1.3530 62.23
21 0.019097 0.010813 2.8117 36.15
25 0.019749 0.010161 2.5993 33.09
  1. SORBITOL.

Temperature \(21^\circ\)C.  Concentration of \(KMnO_4\), alcohol 0.03 M.

\(t\) \(x\) \(a-x\) \(K\) %%
0 0.03046 — 100
2 0.000882 0.029578 0.4792 99.36
6 0.005882 0.024478 1.3148 80.32
8 0.10456 0.020004 2.1450 65.67
10 0.01456 0.015900 3.0063 52.19
12 0.01736 0.013100 3.6255 43.00
14 0.01971 0.011750 3.9336 38.58

Experiments in an alkaline medium.

  1. ETHYLENE GLYCOL.

Temperature \(3^\circ\)C.  Concentration of \(KMnO_4\), glycol, \(NaOH\) 0.03.

\(t\) \(x\) \(a-x\) \(K\) %%
0 0 0.029910 — 100
1 0.000984 0.028926 1.1374 96.71
3 0.002397 0.027513 0.97094 91.99
5 0.003381 0.026529 0.83220 88.70
10 0.004540 0.025370 0.59830 84.82
15 0.005572 0.024338 0.51030 81.37
20 0.006572 0.023338 0.47087 78.03
25 0.007525 0.022385 0.44957 74.84
30 0.008293 0.021617 0.42753 72.29
35 0.009112 0.020798 0.41850 69.53
40 0.009922 0.019988 0.41391 66.83
45 0.010525 0.019385 0.40340 64.81
50 0.011335 0.018575 0.40803 62.10
60 0.012095 0.017815 0.37826 59.66
70 0.013162 0.016748 0.37237 56.00
80 0.013960 0.015950 0.36578 53.45
90 0.014510 0.015400 0.35067 51.49
110 0.015653 0.014257 0.33370 46.53

7. TRIMETHYLENE GLYCOL.

Temperature 3°C.  Concentration of glycol
\(\left.\begin{array}{l}\mathrm{KMnO_4}\\ \text{glycol}\\ \mathrm{NaOH}\end{array}\right\}\) 0,03.

t x a-x K % %
0 0 0,029901 — 100
3 0,001820 0,028081 0,70610 93,94
5 0,002577 0,027324 0,63080 91,38
10 0,003944 0,025957 0,50816 86,81
15 0,004946 0,024955 0,44190 83,46
20 0,005758 0,024145 0,39880 80,74
25 0,006521 0,023380 0,37300 78,19
30 0,006728 0,023173 0,32374 77,50
35 0,007316 0,022585 0,30952 75,53
45 0,008223 0,021673 0,28214 72,50
55 0,009066 0,020835 0,28034 69,69
65 0,010020 0,019881 0,25341 66,49
85 0,010815 0,019086 0,22295 63,85
105 0,011960 0,017941 0,21233 60,00
125 0,012724 0,017177 0,19810 57,45
145 0,013439 0,016462 0,13830 55,05
185 0,013857 0,016064 0,15572 53,72
205 0,015269 0,014632 0,16630 48,94
245 0,015746 0,014155 0,15180 47,34

8. TRIMETHYLENE GLYCOL.

Temperature 17—18°C.  Concentration of alcohol
\(\left.\begin{array}{l}\mathrm{KMnO_4}\\ \text{alcohol}\\ \mathrm{NaOH}\end{array}\right\}\) 0,03

t x a-x K % %
0 0 0,029903 — 100
1 0,001713 0,028190 2,0321 94,26
3 0,003569 0,026234 1,5519 88,06
5 0,004521 0,025382 1,1916 84,86
10 0,006979 0,022924 1,0181 76,66
15 0,008027 0,021876 0,8371 73,16
20 0,009263 0,020640 0,7501 69,02
$t$ $x$ $a - x$ $K$ %%
25 0,010232 0,019671 0,6958 65,78
30 0,010669 0,019234 0,6183 64,32
40 0,011337 0,01757 0,5392 58,76
50 0,012913 0,01699 0,5092 57,08
60 0,013579 0,016324 0,4636 54,60
80 0,015133 0,014870 0,4254 49,73
100 0,015680 0,014223 0,3657 47,57
130 0,016650 0,013253 0,3272 44,32

9. PINACOL.

Temperature 18°C. Alcohol concentration: KMnO₄ — 0,03; NaOH — 0,03.

$t$ $x$ $a - x$ $K$ %
0 0 0,03003 — 100
3²⁰ h 0,00315 0,02688 0,00020458 88,95
4⁵⁰ [[unclear: value]] 0,02542 [[unclear: value]] 86,47
6¹⁰ 0,005870 0,024113 [[unclear: value]] 80,44

10. PINACOL.

Temperature 19–20°C. Alcohol concentration: KMnO₄ — 0,03; NaOH — 0,30.

$t$ $x$ $a - x$ $K$ %
0 0 0,02850 — 100
10 0,000825 0,02775 0,004274 97,11
120 0,002770 0,025780 0,00400 90,29
245 0,004791 0,023759 0,002121 83,22
340 0,006853 0,0217[[unclear: final digits]] 0,00168 76,03
1080 0,014755 0,013855 0,00083 48,39
1200 0,014880 0,013700 0,00075 47,95
1560 0,015551 0,013115 0,00069 45,95

11. GLYCERIN.

Temperature 3 C.
Concentration of alcohol 0.03 mol.

\[ \mathrm{KMnO_4} \]

\[ \mathrm{NaOH} \]

t x a-x K % %
0 0 0,029910 — 100
1 0,007222 0,022688 10,542 75,80
3 0,011128 0,018782 6,603 62,79
5 0,013488 0,016422 5,492 54,90
10 0,016326 0,013584 4,018 45,42
15 0,017442 0,012468 3,113 41,68
20 0,017777 0,012133 2,449 40,56
25 0,017963 0,011942 2,013 39,93
30 0,018110 0,011800 — 39,45

12. ERYTHRITOL,

Temperature 3 C.
Concentration of alcohol 0.03.

\[ \mathrm{KMnO_4} \]

\[ \mathrm{NaOH} \]

t x a-x K % %
0 0 0,029903 — 100
1 0,009915 0,019988 16,581 66,81
3 0,016102 0,013801 13,01 46,15
5 0,017466 0,012437 9,393 41,59

13. ERYTHRITOL.

Temperature 18 C.
Concentration of alcohol

\[ \mathrm{KMnO_4}\quad 0,03. \]

\[ \mathrm{NaOH}\quad 0,003 \]

t x a-x k % %
0 0 0,029910 — 100
5 0,005569 0,024311 0,10674 81,37
15 0,009282 0,020626 0,04297 68,97
25 0,010615 0,019295 0,02693 64,51
35 0,011504 0,018406 0,02018 61,54
55 0,012450 0,017453 0,01353 58,35
95 0,013789 0,016121 0,00850 53,90
175 0,014900 0,015010 0,00494 50,19
335 0,016232 0,013678 0,00283 45,73

14. QUERCITOL.

Temperature 3°C.  Concentration of alcohol 0,03.
\(KMnO_4\)
\(NaOH\)

\(t\) \(x\) \(a-x\) \(K\) %
0 0 0,029903 — 100
1 0,010058 0,019845 16,950 66,37
3 0,015673 0,011230 12,278 47,58
5 0,017577 0,012326 9,559 41,22

15. QUERCITOL.

Temperature 19—18 C.  Concentration of alcohol
\(KMnO_4\) — 0,03
\(NaOH\) — 0,003

\(t\) \(x\) \(a-x\) \(K\) %
0 0 0,029903 — 100
1 0,000778 0,029125 0,44590 97,40
3 0,003189 0,026714 0,16200 89,34
5 0,004775 0,025128 0,10340 84,03
10 0,006679 0,023224 0,05592 77,66
15 0,008233 0,021670 0,03745 73,84
20 0,009503 0,020400 0,02705 68,22
25 0,009693 0,020210 0,02570 67,59
30 0,010296 0,019607 0,02207 65,57
40 0,010710 0,019193 0,01694 64,08
50 0,011311 0,018592 0,01307 62,18
60 0,012136 0,017767 0,01218 59,41
80 0,012675 0,017228 0,01186 57,61
120 0,014357 0,015546 0,00665 51,99
255 0,017434 0,012469 0,00408 41,69

16. MANNITOL.

Temperature 3°C.  Concentration of alcohol 0,03 m.
\(KMnO_4\)
\(NaOH\)

\(t\) \(x\) \(a-x\) \(K\) %
0 0 0,029903 — 100
1 0,010708 0,019195 18,658 64,19
3 0,016633 0,013270 13,968 44,38
5 0,018323 0,011580 10,583 38,73

17. MANNITOL.

Temperature \(3^\circ\mathrm{C}\).

\[ \begin{aligned} \mathrm{KMnO_4} &— 0,03.\\ \text{Alcohol concentration} &— 0,003.\\ \mathrm{NaOH} &— 0,03. \end{aligned} \]

t x a-x K %
0 0 0,029903 — 100
5 0,002333 0,027570 0,09421 92,20
10 0,003411 0,026492 0,04902 88,60
15 0,007171 0,022732 0,04795 76,02
20 0,008393 0,021510 0,03019 71,92
25 0,009598 0,020305 0,02559 67,91
30 0,010327 0,019576 0,02207 65,47
40 0,011406 0,018497 0,02210 61,86
80 0,014293 0,015610 0,01040 52,20
117 0,015626 0,014277 0,00777 47,75

18. MANNITOL.

Temperature \(17—18^\circ\mathrm{C}\).

\[ \begin{aligned} \mathrm{KMnO_4} &— 0,03.\\ \text{Alcohol concentration} & \\ \mathrm{NaOH} &— 0,003. \end{aligned} \]

t x a-x K %
0 0 0,029903 — 100
1 0,000397 0,029506 0,44014 98,67
3 0,002301 0,027602 0,16048 92,31
5 0,006583 0,023320 0,11138 78,00
10 0,009851 0,020052 0,06476 67,06
15 0,010681 0,019222 0,04503 65,78
20 0,012707 0,017196 0,03776 57,51
25 0,013500 0,016403 0,03167 54,85
30 0,014360 0,015543 0,02785 51,99
40 0,015309 0,014594 0,02224 48,81
50 0,016070 0,013833 0,01877 46,26
60 0,016324 0,013579 0,01594 45,41
80 0,017244 0,012659 0,01282 42,33
100 0,018069 0,011834 0,01012 39,58

19. Dulcitol.

Temperature 3°C.
Concentration of alcohol 0.03.

\[ \begin{gathered} \mathrm{KMnO_4}\\ \mathrm{NaOH} \end{gathered} \]

t x a-x K %%
0 0 0.029903 — 100
1 0.009559 0.020344 15.712 62.25
3 0.016498 0.013405 13.720 44.83
5 0.018037 0.011866 10.176 39.68

20. Dulcitol.

Temperature 17°C.
Concentration of alcohol 0.03.

\[ \begin{gathered} \mathrm{KMnO_4}\quad 0.03\\ \mathrm{NaOH}\quad 0.003 \end{gathered} \]

t x a-x K %%
0 0 0.029903 — 100
5 0.006742 0.023161 0.11216 78.92
15 0.012136 0.017767 0.04873 59.41
25 0.014041 0.013862 0.03275 53.04
35 0.015183 0.014720 0.02521 49.23
55 0.016675 0.013330 0.01786 44.24
95 0.017849 0.012054 0.0034 40.31

21. Sucrose.

Temperature 3°C.
Concentration of sugar 0.03.

\[ \begin{gathered} \mathrm{KMnO_4}\\ \mathrm{NaOH} \end{gathered} \]

t x a-x K %%
0 0 0.029903 — 100
1 0.008170 0.021733 12.5710 72.68
3 0.02231 0.017672 6.2735 60.48
5 0.013976 0.015927 5.8704 53.25
10 0.016736 0.013167 4.5046 44.03
15 0.017799 0.012104 3.2784 40.48
20 0.018243 0.011660 2.6160 38.99
25 0.018592 0.011311 2.1987 37.82

As is evident from the tables, calculation by the equation for a bimolecular (and, in the corresponding cases, monomolecular) reaction nowhere gave a good constant. Since in the present work we did not have in mind a detailed elucidation of the reaction mechanism, but only the determination of the relative oxidizability of various compounds, we confined ourselves to comparing the values of \(K\) referring to one and the same stage of permanganate reduction.

Table 22 contains these values (found by interpolation) for stages of the process corresponding to 10%, 20%, and 40% of the active oxygen consumed. Tables 23 and 24 give figures for the relative oxidizability of various alcohols in experiments in neutral (No. 23) and in alkaline (No. 24) solution. All figures are taken for one concentration and reduced to the same temperature. In general, the reaction rate with trimethylene glycol was taken as unity. Only when comparing the results of experiments with concentrations of 0.03 \(KMnO_4\) and 0.003 alcohol and \(NaOH\), the oxidizability of mannitol was taken as 1.

22. RATE CONSTANTS FOR 10%, 20%, AND 40% OF ACTIVE OXYGEN CONSUMED.

Oxidized substances \(KMnO_4\) Alcohol \(NaOH\) Reaction temp. 10% 20% 40%
\(CH_2OH.CH_2.CH_2OH\) 0,03 0,03 — 17,5° 0,02253 0,02117 0,0178
\((CH_3)_2COH.C(CH_3)_2OH^*)\) 0,03 0,03 — 18,5° \((8 \cdot 10^{-5})\) — —
\(C(CH_2OH)_4\) 0,03 0,03 — 21° 1,112 1,967 3,385
Mannitol 0,03 0,03 — 21° 0,583 — 1,469
Sorbitol 0,03 0,03 — 21° 0,658 1,320 2,512
\(CH_2OH.CH_2OH\) 0,03 0,03 0,03 3° 0,8987 0,4940 0,3837
\(CH_2OH.CH_2.CH_2OH\) 0,03 0,03 0,03 3° 0,5038 0,3866 0,2123
\(CH_2OH.CH_2.CH_2OH\) 0,03 0,03 0,03 17,5° 1,703 1,065 0,5568
\((CH_3)_2COH.C(CH_3)_2OH\) 0,03 0,03 0,03 18° \(2,166 \cdot 10^{-4}\) \(2,215 \cdot 10^{-4}\) —
\((CH_3)_2COH.C(CH_3)_2OH\) 0,03 0,3 0,3 19,5° \(3,923 \cdot 10^{-3}\) \(1,924 \cdot 10^{-3}\) \(1,19 \cdot 10^{-3}\)
\(CH_2OH.CHOH.CH_2OH\) 0,03 0,03 0,03 3° — (11,98) 6,210
Erythritol 0,03 0,03 0,03 3° — — 15,34
Erythritol 0,03 0,003 0,003 18° — 0,0997 0,01696
Quercitol 0,03 0,03 0,03 3° — — 15,37
Quercitol 0,03 0,003 0,003 19,5° 0,1852 0,07344 0,01256
Mannitol 0,03 0,03 0,03 3° — — 17,666
Mannitol 0,03 0,003 0,03 3° 0,0666 0,04829 0,0198
Mannitol 0,03 0,003 0,003 16,5° 0,1526 0,1183 0,03995
Dulcitol 0,03 0,03 0,03 3° — — 15,455
Dulcitol 0,03 0,003 0,003 17° — 0,1157 0,05065
Sucrose 0,03 0,03 0,03 3° — (16,466) 6,246

*) The reaction was followed only up to 1,06%.

23. Relative oxidizability of various alcohols in neutral solution*)

Oxidized compounds Relative reaction rate for 10% Relative reaction rate for 20% Relative reaction rate for 40%
$\mathrm{CH_2OH.CH_2OH}$ 0.902 1.01 1.38
$\mathrm{C_2H_5CHOH.CH_2OH}$ 1.71 1.94 2.73
$\mathrm{CH_2OH.CHOH.CH_2OH}$ 1 1 1
$\mathrm{(CH_2OH)_2C(CH_2OH)_2}$ (8.10-) -- --
$\mathrm{CH_2OH.CHOH.CHOH.CH_2OH}$ 2.29 3.57 7.25
$\mathrm{CH_2OH.CHOH.CHOH.CHOH.CH_2OH}$ 11.5 17.1 10.7
$\mathrm{C_6H_{12}O_6}$ 39.4 72.9 155
Dulcitol -- -- 110
Mannitol 20.7 -- 67.1
Sorbitol 23.3 45.2 115

24. Relative oxidizability of various alcohols in alkaline solution

Oxidized compounds Relative reaction rate at a concentration of 0.05 $\mathrm{KMnO_4}$, alcohol, $\mathrm{NaOH}$: [[unclear: first condition]] Relative reaction rate at a concentration of 0.05 $\mathrm{KMnO_4}$, alcohol, $\mathrm{NaOH}$: [[unclear: second condition]] Relative reaction rate at a concentration of 0.03 $\mathrm{KMnO_4}$, 0.003 alcohol and $\mathrm{NaOH}$: 10° Relative reaction rate at a concentration of 0.03 $\mathrm{KMnO_4}$, 0.003 alcohol and $\mathrm{NaOH}$: 10 Relative reaction rate at a concentration of 0.03 $\mathrm{KMnO_4}$, 0.003 alcohol and $\mathrm{NaOH}$: 20° Relative reaction rate at a concentration of 0.03 $\mathrm{KMnO_4}$, 0.003 alcohol and $\mathrm{NaOH}$: 40
$\mathrm{CH_2OH.CH_2OH}$ 1.5 1.5 1.9 -- -- --
$\mathrm{CH_2OH.CHOH.CH_2OH}$ 1 1 1 -- -- --
$\mathrm{(CH_2OH)_2C(CH_2OH)_2}$ [[unclear: number]] [[unclear: number]] -- -- -- --
$\mathrm{CH_2OH.CHOH.CH_2OH}$ -- 51 29 -- -- --
$\mathrm{CH_2OH.CHOH.CHOH.CH_2OH}$ -- -- 72 -- 0.77 0.29
Quercitol -- -- 72 1.08 0.56 0.29
Mannitol -- -- 88 1 1 1
Dulcitol -- -- 75 -- 0.91 1.19
Sucrose -- 15 29 -- -- --

*) In the table, the results of previous experiments are also used (V. V. Tronov, A. A. Fokina, and N. I. Panfilov, l. c.).

Conclusions

1. EFFECT OF THE NUMBER OF ALCOHOL GROUPS.
The rates of oxidation of polyhydric alcohols, both in neutral and in alkaline medium, increase with an increase in the number of alcohol groups. However, the average oxidizability per one alcohol group changes little up to glycerol. A sharp acceleration of the reaction is observed on passing to erythritol, then to pentaerythritol and adonitol. Further on (in the hexitols) the oxidizability again changes little and even seems to decrease somewhat.

2. EFFECT OF THE POSITION OF THE HYDROXYLS IN THE MOLECULE.
a) Tertiary glycols (pinacol) are oxidized much more slowly than primary and primary-secondary ones;

b) primary alcohol groups separated by a \(\mathrm{CH_2}\) link (comparison of glycol and trimethylene glycol) are oxidized somewhat more slowly than when situated next to one another; however, in \(\mathrm{C(CH_2OH)_4}\), with the same groups and also separated by one link, the oxidizability increases extraordinarily.

3. EFFECT OF STEREOISOMERISM is apparently insignificant.
Mannitol and dulcitol in alkaline solution are oxidized at almost the same rate; sorbitol in neutral solution reacted with permanganate somewhat faster than mannitol.

4. SUCROSE, despite the presence of 8 alcohol groups, reacts with permanganate (in alkaline medium) noticeably more slowly than alcohols with 4, 5, and 6 hydroxyls.

5. EFFECT OF THE REACTION OF THE MEDIUM can be seen from Table 25.

25. RATIO OF THE REACTION-RATE CONSTANTS IN ALKALINE AND NEUTRAL SOLUTION.

Oxidized substances Ratio of constants at 10% Ratio of constants at 20° Ratio of constants at 40°
\(\mathrm{CH_2OH.CH_2OH}\) 137 67 44
\(\mathrm{CH_2OH.CH_2.CH_2OH}\) 95 61 39
\(\mathrm{(CH_3)_2COH.C(CH_3)_2OH}\) (23) — —
\(\mathrm{CH_2OH.CHOH.CH_2OH}\) — 223 110
\(\mathrm{CH_2OH.CHOH.CH_2OH}\) — — 270
Mannitol — — 11

As with monohydric alcohols, the addition of alkali, even in an equimolecular amount, increases the reaction rate by tens and hundreds of times. However, the regularity noted earlier—that the more difficult the alcohol is to oxidize, the greater the acceleration—is not justified here. The smallest acceleration coefficient was given by the difficultly oxidized pinacol, the largest by the comparatively readily oxidized erythritol and glycerol; with mannitol the difference again decreased, so that no definite dependence between the effect of alkali and the relative rate of oxidation of the various alcohols can yet be established.

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[v1] 1931

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Rate of Oxidation of Polyhydric Alcohols by Potassium Permanganate