Quantitative determination of mixtures of alkyl ethers of d -glucose

CS'!f s£SS BM SSsk Etsevier Publishing Company, Amsterdam Printed in Belgium

I

QUANTITATIVE DETERMINATION OF MIXTURES OF ALKYL ETHERS OF D-GLUCOSE PART n* . STRUCTURAL STUDIES OF PARTIALLY METHYLATED COTTON CELLULOSE SUSAN

HAwoa:rm, D . M. JoNEs, J. G . ROBERTS, AND B . F. SAGAR

Shirley Institute, Didsbury, Manchester 20 (Great Britain) (Received November 4th, 1968) ABSTRACT

The distribution of methoxyl groups in repeatedly methylated cotton cellulose is in agreement with the suggestion that the elementary fibril is the basic structural element and suggests that a simple model for these elementary fibrils would have an average cross-section of 8 x 10 cellulose chains . The dimensions of such a crosssection are approximately 40 x 50 A and agree closely with electron-microscopical observations . This fibril has a surface in which all of the readily accessible hydroxyl groups lie . Methylation of these hydroxyl groups is quite rapid, but the methylation of hydroxyl groups below this surface takes place at a lower rate . The slower reaction proceeds with little change in methoxyl group distribution, other than the appearance of tri-substituted D-glucose units at a rate similar to that of the disappearance of D-glucose ; it is suggested that this stage of the reaction occurs with an advancing zone of methylation passing through ordered material . Evidence has also been obtained for aggregation of the elementary fibrils . INTRODUCTION

Cellulose has a basically simple molecular structure consisting of D-glucose in extremely long chains. The arrangement of these chains residues linked in native celluloses is complex . In cotton fibres (diameter -10-20 µm), a fibrillar structure (diameter -0.2-0 .3 hum) can be seen by optical microscopy. Electron microscopy, however, reveals still smaller structural elements (diameter 30-60 A) which are termed elementary fibrils . Cellulose chains (diameter - 5 A) make up the elementary fibrils, but their arrangement has not yet been fully determined . In these cellulose chains, only a fraction of the hydroxyl groups are accessible to most reagents unless the cellulose is in solution or is in a very highly swollen state . Studies of chemical reactions of cellulose, such as acid hydrolysis and periodate oxidation, suggest that there are areas of differing accessibility . These have been explained in terms of areas of high order (crystalline regions) and areas of disorder (amorphous regions) . It has, however, become increasingly difficult to explain all *Part I: Ref. 5. Carbnhyd. Res., 10 (1969) 1-12

N

i

r I-• C M t0

0

aG

=

86 71 66 58 51 54 53 46 43

GO

9 9 10 9 9 8 8 7 6

Gs

Moles % of

0 1 1 1 1 1 1 1 1

G3

Go 3 7 8 9 9 9 9 8 8

D-glucose, G2 = 2.O-methyl-D-glucose, etc .

0.20 0.38 0.56 0.71 0.37 0.92 1 .02 ' 1 .08 1 .29

D.S.

treatments

1 2 3 5 8 10 15 20 30

Methoxyl

No. of

1 2 3 3 3 2 2 2 2

G23

2 4 6 8 10 9 9 11 10

G26

0 1 1 1 2 1 1 1 1

Gs 0 3 6 10 14 16 18 22 27

G236

DISTRIBUTION OF METHOXYL GROUPS IN REPEATEDLY METHYLATED COTTON CELLULOSE

TABLE I



12 18 25 31 36 35 37 42 45

at C-2 2 6 11 15 20 20 22 26 31

at C-3 5 13 21 28 35 34 36 41 45

at C6

Hydroxyl groups (%) methylated



STRUCTURAL STUDIES OF METHYLATED COTTON CELLULOSE

3

observations in these terms, and the concept of a fibrillar structure, in which the fibrils may be regarded as crystalline, has gained favour . The structure of cotton cellulose has recently been comprehensively reviewed' . The distribution of methoxyl groups in partially methylated cellulose has been examined previously' but only from the point of view of determining the relative reactivities of the three hydroxyl groups present . In this paper, we describe the use of the measured distributions to obtain structural information on cotton cellulose . RESULTS AND DISCUSSION

Cotton cellulose has been methylated in a repeated treatment which involved soaking in 2N sodium hydroxide, methylation in methyl sulphate-methyl sulphoxide mixtures, washing, and drying . This series of treatments does not lead to extensive swelling of the cellulose as is found with alkali solutions of higher concentration . The extent of reaction was followed by methoxyl determination (Zeisel), either titrimetrically 3 or by a g .l.c. modification' . The variation in degree of substitution in relation to the number of methylation treatments may be interpreted as arising from a reaction occurring in two stages (Fig. 1). An initial rapid reaction, which is largely completed in the first five treatments, is followed by a slower reaction which proceeds steadily over successive treatments . Both infrared-deuteration studies (Fig. 2) and moisture-regain measurements (Fig . 3) indicate that the slower reaction is accompanied by little or no change in accessibility . Thus, the cellulose structure is not being disrupted by any swelling due to methylation during this step . During the initial rapid stage of the methylation, there is an increase in accessibility (13% by infrared deuteration and 8% by moisture-regain measurements) . This initial swelling action is not a uniform swelling of the cellulose structure but is more likely to be the effect of complete water-swelling together with substitution of accessible hydroxyl groups, leading to a complete separation of the surfaces of the ordered structural elements in the cellulose . The identity of the hydroxyl groups in these surfaces was examined by the hydrolysis of the partly methylated cellulose samples taken during the course of the series of repeated methylation treatments and analysis of the resulting mixture of O-methyl-D-glucoses (Table I) . The procedure used was that described in Part I s . The analysis shows that the main products at all stages of the reaction are D-glucose and 2-, 6-, 2,6-di-, and 2,3,6-tri-O-methyl-D-glucoses . The total proportion of the mono- and di-substituted components is approximately constant throughout the later stages of the reaction, suggesting that an advancing zone of methylation is passing through an ordered surface . Initially, the C-2 hydroxyl group is the most reactive (Fig . 4), but, as the reaction proceeds, the extents of methylation at the C-2 and C-6 hydroxyl groups become the same, indicating that equal numbers of these groups are accessible, at least from the eighth methylation onwards. This again suggests that it is an ordered structure which is being methylated . The low reactivity of the C-3 hydroxyl group during the early stages of reaction is noteworthy, and it is Carbohyd. Res., 10 (1969) 1-12



4

S. HAWORTH, D . M. JONES, J . C. ROBERTS, - a. F. SACAR

clearly the least accessible hydroxyl group in the later stages of the reaction . This reduced accessibility can be attributed to the involvement of the C-3 hydroxyl group in an intramolecular hydrogen bond6 to 0-5 . It is clear from the observed distri-

} N

u

J O Q 2 O

O

g S

o

W O

iL0

I 1 10 20 NUMBER OF METHYLATION TREATMENTS

0

30

Fig. 1 . Repeated methylation of cotton cellulose . Fig. 2. Changes in degree of hydrogen-bond order in cotton cellulose on repeated methylation, as measured by an infrared deuteration technique .

0

-0 U K

z -a j r o U25U, U Y7 m 7 h O

0

O

1

50

1 O

2

o " 25

. 0

0

u

N m U

1

m $

s 40 1 I °~ 0 10 20 s

NUMBER OF METHYLATION TREATMENTS

10

20

30

NUMBER OF METHYLATION TREATMENTS

Fig. 3 . Changes in accessibility of hydroxyl groups to water vapour in cotton cellulose on repeated methylation . Fig. 4 . Changes in extent of reaction at individual hydroxyl groups during the repeated methylation of cotton cellulose. Carbohyd. Res., 10 1969 1-12



STRUCTURAL STUDIES OF METHYLATED-COTTON CELLULOSE

butions that reaction at the C-3 hydroxyl group only occurs after the C-2 and C-6 hydroxyl groups have been methylated . This is probably associated with the reduction in intermolecular hydrogen bonding when the C-2 and C-6 hydroxyl groups are substituted ; the steric hindrance to methylation of the C-3 hydroxyl group is thereby reduced . When the proportions of each component are examined in relation to the number of methylation treatments as in Fig. 5 , two stages of change in concentration can be detected, corresponding with the two stages in,change of D .S. degree of substitution . Extrapolation for each component gives the distribution of methoxyl of the D-glucose groups at the end of the initial rapid reaction Table II . Thus, 44 of all of the residues have one or more hydroxyl groups accessible, but only 25 hydroxyl groups are methylated. The main methylated components, viz., 2-, 6-, 2,6-di- and 2,3,6-tri-O-methyl-D-glucose, are present in almost equal amounts .

0

0

a

b-Qucose 0

Tri_O_methyl_p_glucose I I 30 10 20 NVMBER OF METHYLATION TREATMENTS

Fig. 5 . The extent of mono-, di-, and tri-substitution of cotton cellulose during repeated methylation . TABLE II DISTRIBUTION OF METHOXYL GROUPS AT THE END OF THE INITIAL RAPID REACTION IN REPEATED METHYLATION OF CELLULOSE

Moles

Cotton cellulose 2N NaOH-iv1e2SO4--Me2SO Expected distribution on basis of

of

a

G2

56

10

1

10

60

10

--

10

G3

G6

G23

G26

Gs6

G2s6

D.S_

2

10

1

9

0.76

10

0.70

10

model

If the D-glucose arises from residues which are inaccessible by virtue of lying beneath a single layer of accessible residues, and the cellulose chains containing the residues are in a rectangular bundle, then it is possible to calculate the size of models of cross-sections one D-glucose residue thick which would give rise to the observed numbers of inaccessible residues Table III . However, - the cross-sectional model cannot be defined uniquely in this way . Carbohyd. Res., 10 1969 1-12



S. HAWORTH, D . M. JONES, J . G. ROBERTS, B . F. SAGAR

57-42E 555

INACCESSIBLE D-GLUCOSE RESIDUES IN SIMPLE MODEL CROSS-SECTIONS OF VARYING SIZEa

Inaccessible D -glucose residues

No.

of D-glucose

residues

in Side A

12 1_110 9 7 6

55 54 53 52 50 48 44

60 59 57 56 54 51 48

62 61 60 58 56 54 50

65 63 62 60 58 56 52

67 66 64 62 60 57 53

68 67 66 63 61 58 54

69 69 67 65 62 60 55

6

7

8

9

10

11

12

No. Of D-glucose

residues in

side B

aRectangular cross-sections are assumed . In this calculation, a D-glucose residue is assumed inaccessible if not in the surface layer .

Considering the individual D-glucose residues in a cellulose chain which forms part of a surface, the orientation of the D-glucose residues within that surface will dictate the accessibility of the hydroxyl groups . It is to be expected that D-glucose residues lying mainly in the plane of the surface will have a different distribution of accessible hydroxyl groups from those at right angles to the surface . Thus, it can be assumed that the products of methylation of the two pairs of sides of the crosssectional model will be different . If it is assumed that all four major products are not formed in any one side, then the proportions of these components found - 10 of each suggest that the cross-section will be either almost square or have sides in the approximate ratio of 1 :3. From a calculation of the numbers of accessible D-glucose residues in the sides of almost square cross-sections Table IV , it can be seen that equal numbers of D-glucose residues in sides A and B are only given by cross-sections of 11 x 12, 10 x 12, 9 x 11, 8 x 10, 7 x 9, and 6 x 8 . Of these models, all but those of 8 x 10 and 7 x 9 can be discounted as they require quantities of inaccessible D-glucose residues considerably removed from the 56 found experimentally. In the case where the sides are in the approximate ratio of 1 :3, a similar calculation can be made, and cross-sections of 6 x 4, 4 x 14, 9 x 5, 5 x 17, 12 x 6, 6 x 20, 15 x 7, and 7 x 23 would fit this requirement . It is possible to eliminate all but three of these cross-sections 5 x 17, 12 x 6, and 6 x 20 on the basis of their requirement of inaccessible D-glucose residues differing from the 56 found experimentally . The remaining models 5 x 17, 12 x 6, 6 x 20, 7 x 9, and 8 x 10 all have side lengths between 25 A and 100 A, which are within the range of dimensions of the elementary fibril as measured by electron microscopy . Thus, the observed extent of reaction is consistent with the methylation of the elementary fibrillar surfaces . Although the reported observations of the elementary fibrillar dimensions tend to Carbohyd. Res., 10 1969 1- 1 2



STRUCTURAL STUDIES OF METHYLATED COTTON CELLULOSE

7

favour approximately square cross-sections, it is not possible to differentiate between the five most likely models . TABLE IV ACCESSIBLE D-GLUCOSE RESIDUES IN THE SIDES OF SIMPLE MODEL CROSS-SECTION OF VARYING SIZEa

of D-glucose residues in Side A; in Side B

No. OfD-glucose residues in Side A

12 II 10 9 8 6

~

17 ;6 17 ;6 17 ;7 17 ;7 17;8 17 ;10 17;11

14 ;6 14 ;7 14 ;7 14;8 14;9 14 ;10 14;12

13 ;6 13 ;7 13 ;8 13 ;8 13 ;9 13 ;11 13 ;13

11 ;7 11 ;7 11 ;8 11 ;9 11 ;10 11 ;11 11 ;13

10 ;7 10 ;7 10 ;8 10 ;9 10 ;10 10 ;11 10 ;13

9 ;7 9 ;7 9;8 8 ;8 9 ;10 9 ;12 9 ;14

8 ;7 8 ;8 8 ;8 8 ;9 8 ;10 8 ;12 8 ;14

6

7

8

9

10

11

12

No. Of D-glucose residues in Side B aRectangular cross-sections are assumed . Cellulose chains with D-glucose residues common to both sides, i.e., corner units are assumed for the calculation to lie in Side A .

To

define the model more closely, we must further consider the orientation of the cellulose chains . A single cellulose chain has an extended . ribbon-like conformation in which the D-glucose residues are bonded not only by the f3-D- l->4 glucosidic bond but also by the C-3 OH -0-5 hydrogen bond . If the chain lies in the surface of a structural element such that the plane of the surface is at right angles to the plane of the D-glucose residues and along the chain axis i.e., in the 101 crystallographic plane , then on alternate D-glucose residues the C-6 hydroxyl and the C-•2 and C-3 hydroxyl groups would be expected to be accessible . As little 2,3-di-Omethyl-n-glucose has been found, D-glucose residues having both C-2 and C-3 hydroxyl groups accessible cannot be present . If, however, the involvement of the C- •3 hydroxyl group in a hydrogen bond with 0-5 is such that it is rendered inacces-

sible, then the alternate D-glucose residues would be expected to have either C-2 or C-6 hydroxyl groups accessible . In the remaining pair of sides, surfaces containing the anhydroglucose rings i.e., the 101 crystallographic planes might be expected, from consideration of molecular models, to contain D-glucose residues having all three hydroxyl groups accessible to methylation . Closer examination of the models reveals that the C-3 hydroxyl group, if involved in a hydrogen bond with the adjacent 0-5 , would be orientated above and below the surface plane on alternate pairs of n-glucose residues along the cellulose chain . When orientated below the surface, it is in a position which is considerably crowded, particularly when the adjacent C-2 and C-6 hydroxyl groups are methylated Fig . 6 . It is not possible to obtain a complete picture of the molecular alignments in this area due to lack of precise knowledge of the arrangement of parallel cellulose chains, but it is clear that the Carbohyd. Res., 10 1969 1-1 2



8

S. HAWORTH, D. M. JONES, J_ G . ROBERTS, B . F. SAGAR

C-3 hydroxyl group is not readily accessible from the surface and that its methylation would involve some disruption of the structure . Thus, the C-3 hydroxyl group on alternate D-glucose residues along the chain would be expected to be inaccessible to methylation in the initial, rapid reaction, so that equal numbers of D-glucose residues having either C-2 and C-6, or C-2, C-3, and C-6 hydroxyl groups accessible would be found in this pair of surfaces . Thus, four main components are to be expected, equal quantities of 2-, or 6-O-methyl-D-glucose from one pair of surfaces, and equal quantities of 2,6-di- and 2,3,6-tri-O-methyl-D-glucose from the other pair . It is clear therefore that the cross-sectional models based on the 3 :1 ratio of side lengths are not compatible with the expected distribution of methoxyl groups ; this leaves the 7 x 9 and 8 x 10 cross-sections .

Fig. 6. Molecular model of a cellobiose unit in a cellulose chain, showing the relative inaccessibility of the buried C-3 hydroxyl group to methylation .

On balance, the 8 x 10 D-glucose residue cross-section forms the most satisfactory approximation . This model require-2 60 of the D-glucose residues to be inaccessible in the initial, rapid stage of the methylation which is rather higher than the observed value 56 ; any imperfections in the structure would lead to additional methylated products, thus decreasing the total content of D-glucose . More importance is attached to the agreement between the observed total proportion of methylated Carbohyd. Res ., 1 0 1969 1-12



9

STRUCTURAL STUDIES OF METHYLATED COTTON CELLULOSE

and that required by the model 40 components 39 . The size of an 8 x 10 cross-section would be about 40 x 50 A, closely approximating to the lower limit of sire of the elementary fibril observed by electron microscopy . It should be noted that the cross-section of size 8 x 10 is now preferred to that of 8 x 12 previously 9-1.1 . The larger size was, in part, based on the consideration of possibilities quoted of aggregation of such units ; this is now seen to be erroneous, and the 8 x 10 crosssection represents the best fit in terms of the ratio of accessible to inaccessible D-glucose residues and of the distribution of accessible hydroxyl groups in the surfaces . The distribution of methoxyl groups to be expected from this model is as follows . Eight D-glucose residues 10 of the total give rise to 2,6-di-O-methyl-Dglucose and 8 give 2,3,6-tri-O-methyl-D-glucose from the two 8 unit sides, and as the residues common to both pairs of sides are considered to be in the sides containing the most accessible residues, 8 residues 10 give 2-O-methyl-D-glucose and 8 give 6-O-methyl-D-glucose from the 10 unit sides . This distribution is in excellent agreement with that found experimentally Table II . The observed distribution of methoxyl groups can thus be explained in terms of a simple model which is also consistent with the size of the smallest structural elements observed by electron microscopy . This leads to the view that cotton cellulose consists of highly ordered structural elements elementary fibrils containing about eighty chains with those D-glucose residues on the surfaces having accessible hydroxyl groups. Reactions occurring under mild swelling conditions i.e., when cellulose is water swollen proceed most rapidly at the accessible, surface residues in the elementary fibrils. Further reaction at a lower rate occurs below these surfaces . Evidence of aggregation of elementary fibrils has also been found ; presumably, common surfaces are held together by hydrogen bonds which are not broken by weak swelling media. This is shown by repeated methylation of cotton cellulose with diazomethane in ether saturated with water . Reaction in dry ether is extremely slow 12, presumably due to almost complete aggregation of the elementary fibrils in the absence of water . In ether saturated with water, the reaction proceeds rapidly over the first five days by which time, the D .S. is about 0.4 but thereafter much more slowly. The methoxyl distributions in these partially methylated samples Table V indicate that the amounts of the most highly methylated D-glucose residues are now much diminished. Plotting the amounts of the individual components and extrapolating the second portion of each curve gives, as before, the amount of each component at the end of the initial rapid stage Table V . The rapid stage of the methylation by diazomethane is thus seen to be confined of the D-glucose residues . to 13 of all the hydroxyl groups which are situated on 27 Comparing this with the methyl sulphate methylation, where 26 of all of the hydroxyl groups are methylated these being situated on 44 of the D-glucose residues , the number of accessible hydroxyl groups is halved, with the most-exposed D-glucose residues i.e., those giving rise to 2,6-di- and 2,3,6-tri-O-methyl-D-glucose in the methyl sulphate methylation now being less accessible . These results suggest that aggregation is more likely to occur between surfaces which have the most Carbohyd. Res ., 1 0

1969

1-12



5 7 10 15 20 Extrapolated to zero time

2

Reaction period days

G 80 76 73 72 72 72 67 67 73

0.26 0.35 0.40 0.45 0.42 0.43 0.60 0.54 0.39

Moles

Methoxyl D.S.

6 6 6 7 7 7 7 7 7

G2

of G3

6 7 7 8 9 8 9 9 9

Go 2 2 2 2 2 2 2 2 2

G23

3 4 5 5 5 5 6 5 4

1 1 1 2 2 2 2 2 1

G2o Gao 1 2 3 4 3 3 7 7 3

G226

12 14 16 18 16 17 23 21 16

at C-2

metllylated

4 6 7 8 7 8 12 11 6

11 14 16 19 19 18 25 22 17

at C-3 at C-6

Hydroxyl groups

DISTRIBUTION OF METHOXYL GROUPS DURING DIAZOMETHANE METHYLATION OF COTTON CELLULOSE

TABLE V



t7

V

H

0



STRUCTURAL STUDIES OF METHYLATED COTTON CELLULOSE

11

exposed D-glucose residues and which are capable of producing the highest density of hydrogen bonding_ CONCLUSIONS

The change in distribution of methoxyl groups during the repeated methylation of cotton cellulose wet with 2N sodium hydroxide and methylated with methyl sulphate in methyl sulphoxide has suggested that, under these conditions, a structural element of cellulose, namely the elementary fibril, is rapidly methylated on its surfaces . A slower reaction, consistent with a zone of methylation passing through ordered material below the surface, also occurs. The observed distributions can be explained in terms of the simple model of a rectangular bundle of cellulose chains with an average cross-section of 8 x 10 D-glucose residues . The evidence presented here does not permit description of the detailed way in which the chains in the elementary fibrils are arranged, but it is suggested that they are in a regular array . The distribution of the methoxyl groups found in the initial, rapid reaction is compatible with the surfaces expected in such a model . The relative numbers of D-glucose residues having accessible and inaccessible hydroxyl groups are consistent with reaction at the surface of the proposed model . The size of the cross-section 8 x 10 D-glucose residues, i.e., 40 x 50 A, is in good agreement with the dimensions of the elementary fibrils observed by electron microscopy . Reduced accessibility has been found when methylation is by diazomethane in water-saturated ether solution ; it is suggested that one third of the surfaces of the elementary fibrils are rendered inaccessible by aggregation . The observed distribution of methoxyl groups suggests that this aggregation occurs most readily through surfaces containing the largest number of accessible hydroxyl groups . EXPERIMENTAL

Methylation of cotton cellulose with methyl sulphate . - Cotton cellulose in fabric form 6 x 6", N 35 g was pretreated by soaking in 2N sodium hydroxide for 45 min and then immersed in a mixture of methyl sulphate 25 ml and methyl sulphoxide 50 ml for a further 45 min . [These two operations were conveniently carried out on a laboratory-scale jig Horsefall Engineering Ltd ., Rochdale, Lancaacetic acid, washed in warm shire .] The samples were then rinsed in warm 60° 1 60° water for 1 h, and immediately dried at 90 ° without any intermediate cooling. The treatment was repeated up to 30 times, samples being taken at intermediate steps . Methylation of cotton cellulose with diazomethane . - Diazomethane was prepared" in ether solution from N-methyl-N-nitroso p-toluenesulphonamide . The strength of the solution prepared was ca. 0.25M. Cotton cellulose in fabric form 2" x 1 ", N 300 mg was suspended in diazomethane dissolved in ether saturated with water and kept for 24 h at 0° . The diazomethane solution was replaced daily. Fabric samples were taken at intervals during treatment for 1 to 20 days. Carboliyd. Res., 10 1969 1-12



12

- S. HAWORTH, D . M. JONES, J. G. ROBERTS, B . F. SAGAR

Cotton cellulose. - The sample of cotton cellulose was in fabric form . It had been scoured and bleached to remove non-cellulosic impurities . Distribution of methoxyl groups. - Analyses were carried out in the manner described in the previous papers . Infrared deuteration and moisture regain. - Accessibility measurements using these techniques were made in the manner described previously" ACKNOWLEDGMENTS

This work was financed in part by the United States Department of Agriculture under P.L. 480. Mr. R. N. Robinson is thanked for preparing the samples of methylated cellulose . REFERENCES I J . 0 . WARWICKER, R . JEFFRIES, R. L. COLBRAN, AND R . N. RCi3 NSON, Shirley Institute Pamphlet, No . 93 1966 25. 2 1 . CROON, Svensk Papperstid., 63 1960 247. 3 E. P . Sn+ISEL AND J . A . McHARD, Ind. Enu. Chem ., Anal. Edn ., 14 1942 750. 4 H. R . COOPER, J. G . ROBERTS, AND R . P . SAGAR, in preparation . 5 S . MAWORTH, J . G. ROBERTS . ?..d B. F. SAGAR, Carbohyd. Res., 9 1969 491 . 6 C. Y . LIANG AND R. H. :MIARCHESSAULT, J. Polymer Sci ., 37 1959 385 . 7 Ref. 1, p. 28. 8 D. A . REES AND R . J . SKERRETn, Carbohyd. Res., 7 1968 334. 9 S. HAWORTH, J. G . ROBERTS, AND R . N . ROBINSON, Textilveredlung, 2 1967 361 . 10 R . JEFFRIES, J . G. ROBERTS, AND R . N . ROBINSON, Textile Res. J., 38 1968 234. 11 R . JEFFRIES, D. M. JONES, J. G . ROBERTS, K. SELBY, S . C. SIMMENS, AND J. 0. WARWICKER, Cellulose Chem . Tech., to be published . 12 F. S . H . HEAD, J. Textile Inst., 43 1952 T1 . 13 J . DE BOER AND H. J . BACKER, Rec. Trav . Chim., 73 1954 229. Carbohyd. Res., 10

1969

1-12