Chemistry Everyday for Everyone

Vanillin: Synthetic Flavoring from Spent Sulfite

Liquor1
Martin B. Hocking
Department of Chemistry, University of Victoria, P.O. Box 3055, Victoria, BC V8W 3P6, Canada

Abstract

Separation of the lignin component of wood from the cellulose presents an opportunity to access various interest-ing products from
the lignin fragments. The lignin represents availability of a sizable renewable resource. Vanillin, or 3-methoxy-4-hydroxybenzaldehyde,
is one of a series of related substituted aromatic flavor constituents, and repre-sents one of the potentially profitable possibilities. Vanillin
production from the lignin-containing waste liquor ob-tained from acid sulfite pulping of wood began in North America in the mid
1930's. By 1981 one plant at Thorold, Ontario produced 60% of the contemporary world supply of vanillin. The process also
simultaneously decreased the organic loading of the aqueous waste streams of the pulping process. Today, however, whilst vanillin
production from lignin is still practiced in Norway and a few other areas, all North American facilities using this process have closed,
primarily for environmental reasons. New North American vanillin plants use petrochemical raw materials. An inno-vation is needed to
help overcome the environmental problems of this process before vanillin production from lignin is likely to resume here. Current
interest in the promotion of chemicals production from renewable raw materials rein-forces the incentive to do this.

Keywords

Organic Chemistry
Public Understanding/Appreciation
Consumer Chemistry
Industrial Chemistry
Food Science
Natural Products

Supplementary Materials

No supplementary material available.

Full Text Return to Table of Contents

Vol. 74 No. 9 September 1997 • Journal of Chemical Education

Abstract
 Chemistry Everyday for Everyone

cinnamaldehy
de b.p. 248 °C

cinnamon

OH

eugenol
b.p. 254 °C

oil-of-cloves

Figure 1. Structural relationships between a group of

important flavor es-sences and a perfume ingredient. True
jasmine scent from jasminal is less intense than from the
derivative illustrated here and does not have the aro-matic
Vanillin: Synthetic Flavoring from Spent Sulfite
Liquor1

Martin B. Hocking
Department of Chemistry, University of Victoria, P.O. Box 3055, Victoria, BC V8W 3P6,
Canada
 Vanillin is the chief constituent of natural vanilla CHO CHO CHO
CO2CH3
flavoring, used in foods for centuries. Cortez is said to CHO

have been served a chocolate drink flavored with va- OCH3 OCH2CH3

nilla by the Aztecs in about 1520. He brought the OH OH OH

knowledge of both chocolate and vanilla back to Spain 2 3 4 5

and Europe, where they rapidly became popular. Use of benzaldehyde vanillin ethyl vanillin (or methyl

natural and synthetic vanilla as flavorings has con-tinued b.pb. 178 °C m.p. 81–83 °C
vanillal)
m.p. 77–78 °C
salicylate
b.p. 222 °C
to grow since then; by 1850 their household use was so almond vanill vanilla ´ 3.5 wintergreen
a
common that they inspired the quotation “Ah, you flavor H CHO
everything; you are the vanille of society” (1). Today,
vanillin, as vanilla flavor, and methyl sali-
N O
cylate, as wintergreen flavor, are the largest-volume CH2 CH3 CH3
O
synthetic food flavorings in common use. H3C CH3

Structurally vanillin, or 3-methoxy-4-hydroxy- OCH3 OCH3 OCH3 OCH3

benzaldehyde (3) and methyl salicylate (5) are mem-bers OH OH OH

7 8 9
of a group of flavoring and essence compounds all with zingerone capsaicin cinnamaldehyde
related structures (Fig. 1). Ethyl vanillin (4), the meta- derivative

ethoxy analog of vanillin, is also used com-mercially as a m.p. 40–41 °C

ginger
m.p. 62–65 °C
hot pepper
b.p. ca. 190 ° @ 20 mm
jasmine scent
vanilla flavoring; it has about 3.5 times the flavor
(1000 ´
intensity of vanillin itself. It is intriguing to observe the zingerone)

minor structural differences among these materials and with warm aqueous ethanol (35% v/v) may be used to pro-duce
speculate on the factors respon-sible for the shift in flavor natural vanilla flavoring. Flavor contributions from the bean
from the relatively mild to sweet varieties used in bakery itself are obtained by direct extraction of the bean using the
goods and confection-ery, such as almond and vanillin, to warm fluids used in baking or other cookery. How-ever, the
the more intensely flavored zingerone, the chief flavor brown solution of natural vanilla as an extract in aqueous
component of the ethanol is a form more convenient to use for many purposes
sweet or savory uses of ginger, to the 1000+ times more po-tent (Table 1).
capsaicin, the principal “hot” flavor constituent of cay-enne,
jalapeño, and habañero peppers. Capsaicin is also the chief
active ingredient in the oleoresin capsicum, used in pepper Table 1. Concentrations of Principal Aromatic
sprays and marketed at 2% strength for personal de-fensive use Polar Compounds in Natural Vanilla Extracta (5 )
1
(3 /2–5% to discourage aggressive dogs, and 10% as a bear Constituent Concentration
repellent [without guarantee]). (mg/100 mL)
Vanillin occurs widely in nature in trace amounts in the
Vanillin 135–175
woody tissues of plants, as well as in commercial products such
4-Hydroxybenzaldehyde 10–12
as tobaccos (2–4). The characteristic aroma of vanillin is very
noticeable from the bark of the ponderosa pine (Pinus Vanillic acid 7–8.5
ponderosa). The highest natural concentrations, 1–3% and 4-Hydroxybenzoic acid 1.5–3.3
sometimes higher, are found in the properly cured pods of the
a
“vanilla bean”. Vanilla beans are harvested from species of the Natural vanilla extract is defined as containing
Vanilla orchid, a tropical climbing plant that derives all its the extract-able matter of 13.35 oz of vanilla beans
(having a maximum moisture content of 25% w/w)
sustenance from the air and rainfall. The vanillin in the green
per U.S. gallon of 35% (v/v) ethanol in water (5).
bean as picked is tied up as the glucoside, and hence does not
have the telltale smell of vanillin at this stage. But after the
proper maturation processes of drying and warmth causing
“sweating”, the vanillin glucoside, 10, is en-zymatically
hydrolysed to glucose, 11, and vanillin, 3 (eq 1).

H H

HO
CH2OH
H
CH2OH
H
(1) Vanillin Isolation, Preparation
O O CHO HO O CHO
OH HO
HO HO
H H3CO H +
H3CO
Gobley, in 1858, was the first to isolate and identify the
H HO
H HO
vanillin constituent of the vanilla bean and to confirm that this
H H
was the chief flavor component (6, 7). The high prices, plus the
10 11 3
vagaries of weather that affect the volume of va-nilla beans
produced each year, provided a strong stimulus for the
The bean, at this stage brown and somewhat shriveled, is now preparation and marketing of synthetic vanillin as a supplement
readily recognized by smell as a source of the popular vanillin to natural sources. In 1874–75, less than 20 years from its initial
flavor. Either the cured bean itself or its extract isolation, synthetic vanillin prepared
Vol. 74 No. 9 September 1997 • Journal of Chemical Education

1055
 Chemistry Everyday for Everyone

from eugenol, 12, became available in France and the United illin yields as high as 10% using air or 20–30% using ni-
States and sold for U.S. $176 per kilogram (8) (eq 2). trobenzene as the oxidant were possible in the laboratory (15).
The higher yields possible with nitrobenzene were com-
mercially unattractive because of the need to deal with the co-
CHO produced nitrobenzene reduction products.
CH2 CH3
KOH oxidati (2)
on CHO CHO
OCH3
OCH3 OCH3 CH2 CH2 CHO
(3)
OH OH OH
H C SO3H H C OH
12 13 3 NaOH oxidation
+ CH3CHO
eugeno isoeugenol vanillin in
l water OCH3
OCH3 OCH3
OH OH OH
sulfonated 3
With vanilla beans of only 1–3% by weight vanillin selling for
US $5.50–8.00 per kilogram—that is, $180–800 per kg of lignin vanill acetaldehyde
vanillin content, this was still competitive. Eugenol from oil of in
cloves continued to be a starting material for synthetic vanillin fragment
production until at least the 1920s (9).
The first hints that it might be possible to produce van-illin Commercial Vanillin from Lignin
from lignin-containing wastes came from an anony-mous report
in 1875 of a vanillin-type smell in spent acid sulfite pulping Production-scale preparation of vanillin from the lignin of
liquor, confirmed by Grafe on his pyrolysis of dried waste sulfite waste sulfite liquor began in the United States in 1936 as a joint
liquor (10, 11). This possibility was better established by the venture of the Salvo Chemical Corp. and Mara-thon Paper Mills
detailed research of Howard and others in the United States (12), Co. of Wisconsin, using the technology de-veloped by Howard
and at McGill University by Tomlinson and Hibbert (13, 14). (16). A year later Howard Smith Paper Mills Ltd. began the first
Howard patented meth-ods to concentrate the required lignin Canadian production-scale plant at Cornwall, Ontario, based on
fraction of the pulping waste, an important preliminary. The the research work conducted at McGill (17, 18). Further studies
McGill group found that the yield of vanillin varied somewhat by Ontario Pulp and Pa-per in the 1940s led to the construction
with the source of the liquor and with the degree of lignin of a second Cana-dian vanillin-from-lignin production unit on
sulfonation. They proved that up to 2.6 g/L of vanillin (up to
the scale of 227,000 kg per year at Thorold, Ontario in 1945.
5.9% of the lig-nin content) could be recovered from waste
Integral with the vanillin operation of this plant was an initial
sulfite liquor (eq 3). Freudenberg showed a little later that
lignin-based van- fer-mentation step that could make use of the 3–5% ferment-
Figure 2. Integration of a
fermentation plant, and vanillin
preparation for spent liquor val-ues
from an acid sulfite pulp mill, as
adapted from a company brochure.
The annual produc-tion values given
are estimated from produc-tion rates
reported for Ontario Pulp and Pa-per
at Thorold (21, 22), as follows:
pulp, 270 air-dry tons per day ´ 350
6
d/yr ´ 500 Can $/ton = 47.25 ´ 10
$/yr
5
ethanol (96%), 8.0 ´ 10 Imp gal/yr
6
´ 3.75 Can $/Imp gal = 3.024 ´ 10
$/yr;
6
vanillin, 3.4 ´ 10 kg/yr ´ 15 Can
6
$/kg = 51 ´ 10 Can $/yr;
saltcake, Na2SO4/ca. 30% Na2CO3, (5–
5 6
8) ´ 10 ton/yr ´ 0–70 Can $/t = 0–10
Can $/yr.
1056 Journal of Chemical Education • Vol. 74 No. 9
September 1997
 Chemistry Everyday for Everyone

Table 2. Trends for Natural Vanilla Beans and Synthetic Vanillin in U.S. Market
able sugars commonly present in spent acid sulfite pulping
(a)
liquors before vanillin production and recovery (Fig. 2). Af-ter
making the “fermentation black liquor” alkaline and oxi-dation
with air at 160–170 °C and 10–12 atm pressure, the oxidation
product stream was extracted with toluene and then back-
extracted with aqueous sodium hydroxide. The aqueous solution
of crude sodium vanillate (14) obtained in this way was then
purified via the carbonyl sulfite addition compound by addition
of aqueous sulfur dioxide (eq 4). The soluble addition compound
of vanillin (15) was thus readily separated from acetovanillone
(14) and other insoluble phe-nolic impurities by filtration. To
produce a food-grade prod-uct the vanillin was then
reprecipitated from this aqueous solution by neutralization and
vacuum-distilled, with a fi-nal purification by crystallization.
Full quantitative details of an early version of this process have
been published (19).
CHO
HO CHSO3Na COCH3
(4)
+H2SO3
,
OCH3 OCH3 OCH3
ONa OH OH
14 15 16
sodium sulfite acetovanillone
addition (b)
vanilla compound
te

The vanillin production of Ontario Pulp and Paper be-came

such a valuable component of their operations that the scale was
gradually expanded to 3.4 million kilograms per year by 1981,
sufficient to supply 60% of the then cur-rent world market. This
also began to subtly affect the pulping component of their
business.
The vanillin recoverable on the proper processing of waste
sulfite liquor is produced from guaiacyl units (18) of the lignin
(17), which is sulfonated and solubilized during the pulping of
wood for the production of chemical pulps. When the raw wood
used for pulping is coniferous in origin, the bulk of the
appropriate building blocks in the lignin are guaiacyl, and the Figure 3. (a) Lignin model segment adapted from
dominant aldehyde product on alkaline oxidation of the partially
Hocking (20).
sulfonated lignin is vanillin (3) (Fig. 3). In contrast the
appropriate building blocks in the lignin of deciduous woods (b) A generalization of the respective pathways to
comprise mostly syringyl units (19) with only a relatively small vanillin from a softwood (coniferous) lignin, and a
proportion of guaiacyl units. Consequently alkaline oxidation of mixture of syringaldehyde plus vanillin from a
the spent sulfite liquor from the pulping of deciduous woods hardwood (deciduous) lignin.
gives mostly syringaldehyde and lower yields of vanillin.
Realizing this,
Ontario Pulp and Paper trucked coniferous
wood from greater distances rather than use
closer supplies of deciduous wood for
pulp production, in order to keep their yields of Year Natural, as Beans
a
Synthetic, as
vanillin from the waste liquor high. This Vanillin
b
represents a prime example of the feedstock of
Metric U.S. $/kg Ref Metric U.S. $/kg Ref
an industrial operation being influenced as
much or more by a “waste stream” product as Tons Tons
by the primary product, in this case the 1874 – 5.50 8 – 176 8
chemical pulp destined for use in newsprint 1913 363 – 8 0.025 – 8
production—a case of “the tail wagging the 1924 360 19.80 8 – 18 8
dog”!
The chemistry of vanillin recovery from 1934 360 7.70 8 – 6 8
lignin is an interesting reflection of the oxi- 1938 360 – 8 206 8.80 8
dation-stabilizing contributions of the hy- 1951 – – 453 6.60–9.00 19
droxyl and one or two methoxyl substitu-ents
for the two aromatic aldehydes, vanil-lin and 1971 – 11.00–18.50 24 – 11 25
syringaldehyde. While these alde-hydes are 1980 – 88–101 24 – 11–12 25
slowly oxidized by air, without this substituent 1991 498 33.30 24 4500–5500 11–14 25
stabilization the recovery conditions used
1992 437 27.60 24 4500–5500 11–14 25
would lead to rapid oxida-tion of these
products to the corresponding vanillic and a
Of 1–3% vanillin content. Price is subject to wide fluctuations both month-
syringic acids, 18 and 19, R = carboxyl, of less to-month and from quality/source considerations (e.g., Madagascar, Tahiti, Java,
value as flavor constituents. Mexico, Indonesia). Prices quoted are intended only as representative.
b
Major current world producers of vanillin and their estimated capacities in
metric tons per year are: Rhône-Poulenc, 4500; EuroVanillin, 2300; Chinese
producers, >454; Ube Industries (Japan), ca. 204; Wlocvavek Plant (Poland), ca.
50 (25–27).
Vol. 74 No. 9 September 1997 • Journal of Chemical Education

1057
 Chemistry Everyday for Everyone

Figure 4. Outlines of petrochemical options to vanillin, 3, starting with benzene.

Quantitative details of pathway (a) have been published (29).
 a
Table 3. The Shift in Uses of Vanillin with Time
Time Use Example
1960 Flavoring (~85%) Beverages, 200 ppm
Bakery products, 1900 ppm
Ice cream, 3000 ppm
Candy, 4000 ppm
Masking fragrance, industrial Paint, to mask odors during drying,
products 500 ppm
1970 ® Chemical intermediate for syntheses Papaverine (treatment of heart
(>50%) problems)
Hydrazones (2,4-D-like herbicides)
Antifoam (lubricating oil additives)
L-Dopa(Parkinson's disease
treatment)
L-Methyldopa (antihypertensive drug
Aldomet)
Trimethoprim (antibacterial agent)
a
Note that vanilla beans and genuine vanilla extract remain almost exclusively in use as a
flavoring because of cost.
1058 Journal of Chemical Education • Vol. 74 No. 9
September 1997