|Molecular formula||C 8 H 8 O 3|
colorless needles smelling of vanilla
|External identifiers / databases|
|Molar mass||152.14 g mol −1|
1.06 g cm −3 (20 ° C)
0.29 Pa (25 ° C)
|pK s value||
7.40 (25 ° C)
|As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .|
Vanillin ( 4-hydroxy-3-methoxybenzaldehyde , FEMA 3107 ) is the main flavoring substance in the capsule fruits of the spice vanilla ( Vanilla planifolia ) as well as a nature-identical flavoring substance . The organic chemical compound with the empirical formula C 8 H 8 O 3 is a derivative of benzaldehyde with an additional hydroxyl and methoxy group .
Vanillin is the main component of natural vanilla extract , a mixture of several hundred different compounds. Vanillin was isolated from this rather rare natural product as early as the middle of the 19th century, and in 1874 the first synthesis from the natural substance coniferin was achieved . The first commercial manufacturing processes for vanillin later came from eugenol . Today vanillin is as nature-identical cost of guaiacol synthesized or from lignin recovered, a constituent of wood and the most common byproduct of industrial pulp production . The vanillin in the lignin also contributes to the typical smell of old paper. In addition, several biotechnological processes have now been established whose products can be declared as "natural".
In terms of quantity, vanillin is the most important flavoring substance worldwide , and it can also be produced cheaply. It is used in food, beverages, ice cream, baked goods and chocolate, as well as in the perfume and pharmaceutical industries.
Vanilla was grown as a flavor by pre-Columbian peoples of Central America; at the time of their conquest by Hernán Cortés , the Aztecs used them as a flavoring for chocolate . Both chocolate and vanilla became known to Europeans around 1520.
Vanillin was first isolated as a relatively pure substance by Nicolas-Théodore Gobley in 1858 ; this was done by complete evaporation of a vanilla extract and subsequent recrystallization from hot water. In 1874, the chemist Wilhelm Haarmann, together with Ferdinand Tiemann, succeeded in producing vanillin from coniferin , which occurs in the bark sap of conifers , for the first time in Holzminden .
In 1876 Karl Reimer synthesized vanillin ( 2 ) for the first time from guaiacol ( 1 ). In the synthesis, later called the Reimer-Tiemann reaction , guaiacol is reacted with chloroform in an alkaline medium . First, chloroform reacts with the base to form dichlorocarbene . This settles the phenolate - anion to the guaiacol.
Vanillin is found most often in the capsule fruits of the spice vanilla ( Vanilla planifolia ) (1.5–4%), which are usually incorrectly referred to as pods , and also in styrax , cloves and other plants. The freshly harvested green seed pods contain vanillin in the form of its β- D -glucoside vanillosid . The green pods do not have the taste or smell of vanilla. Relatively pure vanillin can deposit as white dust or "frost" on the outside of the pods.
In lower concentrations, vanillin contributes to the taste and aroma of foods in a number of ways: in olive oil , butter, raspberries and lychee fruits. Vanillin also contributes to the flavor profile when wines and spirits are matured in oak barrels . In other foods, heat treatment creates vanillin from other existing ingredients. In this way, vanillin contributes to the taste and aroma of roast coffee , maple syrup and whole grains, including corn tortillas and oatmeal.
Extraction and presentation
The up to 30 cm long capsule fruits of the spiced vanilla are harvested shortly before ripening. These do not yet have the typical aroma and taste of the finished product. To obtain it, the fruits are subjected to what is known as black browning. First the capsule fruits are treated with hot water or steam, followed by fermentation in airtight containers. The drying and fermentation processes transform the β- D -glucosides of vanillin into vanillin and glucose .
A large part of the vanillin is obtained from the sulphite waste produced during pulp production . The lignosulphonic acid contained therein is treated with oxidants and alkalis at elevated temperature and pressure , whereby among other things vanillin is formed, which is purified by extraction , distillation and crystallization . The yields are 7–25% depending on the type of wood. This artificial vanilla flavor based on lignin has a richer taste profile. This is due to the presence of acetovanillon as a lignin by-product - an impurity that does not occur in vanillin from a guaiacol synthesis.
- Vanillin can be technically isomerization of eugenol ( 1 ) to isoeugenol ( 2 ) by means of alkalis, followed by oxidation by potassium permanganate or ozone gain.
- A laboratory-scale synthesis is carried out by electrophilic bromination of 4-hydroxybenzaldehyde ( 1 ) to 3-bromo-4-hydroxybenzaldehyde ( 2 ), followed by a copper-catalyzed methoxylation to vanillin ( 3 ):
- Using the Vilsmeyer-Haack synthesis , vanillin is obtained from guaiacol in about 70% yield. Guaiacol and N -methylformanilide react in the presence of phosphorus oxychloride as a catalyst to form vanillin.
- Guaiacol can be converted into vanillin and metanilic acid with formaldehyde and 3-nitrobenzenesulfonic acid in a process that takes several days .
- Another option is the substitution reaction of guaiacol ( 1 ) with glyoxylic acid and subsequent oxidation of the formed vanillylmandelic acid ( 2 ) to 4-hydroxy-3-methoxyphenylglyoxylsäure ( 3 ) to vanillin ( 4 ) is decarboxylated is.
- Another frequently used method is the Fries rearrangement of guaiacol acetate into acetovanillon and its subsequent degradation to vanillin.
Alternatively, various biotechnological methods are available. Vanillin can be produced from ferulic acid, for example, by Amycolatopsis or Streptomyces strains . Ferulic acid can also be produced biotechnologically with the help of Pseudomonas strains from eugenol in a fed-batch process (eugenol is toxic to the cells). Eugenol is a readily available raw material and comes from clove oil. Curcumin also serves as a precursor to vanillin, with the help of the bacteria Rhodococcus rhodochrous this is obtained through biotransformation . It is also possible to obtain it from glucose using genetically modified Escherichia coli bacteria and subsequent dehydrogenase .
It can also be produced from yeast cultures via the shikimic acid route .
Vanillin as a product of the shikimic acid pathway ( 1 ). The end products of this path of chemical reactions are the amino acids phenylalanine , tyrosine and tryptophan . Phenylalanine ( 2 ) is biosynthetically converted to cinnamic acid ( 3 ) with the help of the enzyme phenylalanine ammonia lyase (PAL) with the release of ammonia (NH 3 ) . This is the first step in the biosynthesis of the phenylpropanoids .
Two main ways are under discussion how the steps to vanillin proceed on the basis of phenylpropanoid compounds : the ferulic acid route and the benzoate route . Both initially assume a p -hydroxylation of cinnamic acid to p -cumaric acid (4- hydroxycinnamic acid ) ( 4 ). This is followed by three reaction steps, the order of which is different, but ultimately leads to the target molecule.
- In the ferulic acid pathway , hydroxylation takes place at the 3-position in the ring to form caffeic acid ( 5 ) and then its methylation to ferulic acid ( 6 ), and finally the double bond is cleaved to form the aldehyde , vanillin ( 7 ).
- In the benzoate route , however, the double bond is first cleaved to form 4-hydroxybenzaldehyde ( 8 ), then hydroxylation at the 3-position in the ring to form protocatechualdehyde ( 9 ) and finally its methylation to vanillin ( 7 ).
The hydroxylations from 3 to 4 and from 8 to 9 are catalyzed by the enzyme diphenolase . In the latter reaction, diphenolase acts as monophenol oxidase ; this activity currently has a different EC number ( EC 184.108.40.206 ), but it is the same enzyme.
In contrast to chemical production (“nature-identical”), the biotechnologically produced vanillin can be declared as “natural”.
Biosynthetic vanillin is around 60 times more expensive than synthetic (2015) but still cheaper than natural.
Vanillin occurs in the form of colorless, characteristically sweet-smelling needles, which gradually oxidize to vanillic acid in moist air . It dissolves poorly in water (10 g / l at 25 ° C.), on the other hand, in ethanol and diethyl ether . The compound occurs in two polymorphic crystal forms. Form I melts at 82 ° C with a heat of fusion of 22.4 kJ mol −1 . It crystallizes in the monoclinic crystal system in the space group P 2 1 (space group no. 4) with the lattice parameters a = 1404.9 pm , b = 787.4 pm, c = 1501.7 pm, β = 115.45 ° and four Formula units per unit cell . Form II melts at 80 ° C with a heat of fusion of 20.7 kJ mol −1 . Both crystal forms are monotropic to one another, with Form I being the thermodynamically stable crystal form. Vanillin boils at 285 ° C at normal pressure in a CO 2 atmosphere or 154 ° C at negative pressure (13 hPa ).
The substance is structurally derived from both benzaldehyde and guaiacol ( 2-methoxyphenol ). Due to its bifunctional character, vanillin is very reactive. A large number of derivatives can be synthesized by etherification , esterification or aldol condensation . Further reactions are possible by attacking the aromatic ring. A catalytic hydrogenation of vanillin leads to vanillyl alcohol or 2-methoxy-4-methylphenol . Vanillin can be enzymatically oxidized to vanillic acid. An aqueous solution of iron (III) chloride forms a blue-violet color with vanillin.
The pK s value of the phenolic OH group is 7.40 (25 ° C). At 9.99 this value is significantly lower than for phenol; the electron-withdrawing aldehyde group increases the OH acidity through its −M effect ; the phenolic OH bond is increasingly polarized. The pK s value of the 4-hydroxybenzaldehyde is moving at a similar value and amounts to 7.66; the lack of a methoxy group makes little difference here. For comparison, the guaiacol has ( 2-methoxyphenol ) with its pK s practical value of 9.98 no difference to the phenol with 9.99.
Isomers and structural relatives
Isovanillin ( 3-hydroxy-4-methoxybenzaldehyde ) is an isomer and differs from vanillin in the position of the methoxy group. Instead of position 3, this is found here in position 4. Hydroxy and methoxy groups swap places compared to vanillin.
ortho- vanillin ( 2-hydroxy-3-methoxybenzaldehyde ) is also an isomer and differs from vanillin in the position of the hydroxyl group. The prefix ortho indicates the position of the hydroxyl group in the substitution pattern with respect to the aldehyde group; in vanillin these two groups are in para position.
Ethylvanillin ( 3-ethoxy-4-hydroxybenzaldehyde ) is structurally related and differs from vanillin in that the methyl group is exchanged for an ethyl group. It does not occur naturally, but is produced by synthesis. Today it is often used as an artificial flavoring instead of the more expensive vanillin, as it costs about half as much and is two to four times more intense in taste and aroma.
Acetovanillon ( 4-hydroxy-3-methoxyacetophenone , also apocynin ) is also structurally related and differs from vanillin in that the aldehyde group is exchanged for an acetyl group . It is created in artificial vanilla flavors based on lignin .
Vanillin and ethylvanillin have a similar odor, but that of isovanillin is hardly noticeable. Vanillin and ethylvanillin can be easily separated using mixtures of hexane and ethyl acetate by thin-layer chromatography .
Veratrumaldehyde ( 3,4-dimethoxybenzaldehyde ), also methylvanillin, is also a structural relative with the same molecular formula.
Propenylguaethol (Vanitrope) is also used as a substitute; it has a typical vanilla aroma and its smell is about 15 times more intense than that of vanillin.
The reliable qualitative and quantitative determination of vanillin in different test materials is possible after sufficient sample preparation by using gas chromatography or HPLC coupled with mass spectrometry .
The determination of vanillin can also be used to check the quality grades of olive oil as a marker substance. This analytical use to check authenticity in extremely fatty matrix, however, requires special procedures.
In terms of quantity, vanillin is the most important flavoring substance worldwide, not least because it can be manufactured at low cost. A consumption of around 15,000 tons per year is assumed (2004). The approximately 2,000 tons of capsule fruits of real vanilla , which are harvested worldwide every year, contain only about 40 tons of vanillin (the vanillin content of a commercial vanilla pod is between 1.6 and 2.4% according to ISO standard 5565-1: 1999). So over 99.7% of the vanillin placed on the market is not of natural origin.
Vanilla sugar is a preparation with the natural vanilla flavor of at least 1 g of ground vanilla pods or their extracts to 16 g of sugar ( sucrose ), vanilla sugar contains the flavoring addition of at least 0.17 g of vanillin to 16 g of sugar. Vanillin is used as a flavoring in various foods , including ice cream , baked goods, and chocolate . In addition, vanillin is one of many fragrances in perfume production and to improve the taste of pharmaceuticals and vitamin preparations , where it is used in small quantities to round off and fix sweet, balsamic scents.
Vanillin is also used in the chemical industry, for example as a starting material or intermediate in the synthesis of various medicinal products such as levodopa , methyldopa and papaverine . It is also part of Günzburg's reagent - an alcoholic solution of phloroglucin and vanillin for the qualitative detection of free hydrochloric acid in gastric juice .
Vanillin is used in histology in vanillin HCl staining to stain tannins . Vanillin can be used as a detection reagent for the derivatization of compounds in thin layer chromatography . The developed plate is wetted and heated by spraying or dipping with a vanillin-sulfuric acid solution. Some compounds show characteristic color reactions by means of which they can be identified.
More reactions and enzymes
- Vanillin dehydrogenase - enzyme that catalyzes vanillin to vanillic acid
- Vanillin Synthase Catalysis
- Vanillyl alcohol oxidase - enzyme that catalyzes various phenolic compounds through oxidation
- Vanillate monooxygenase - catalysis from vanillate to protocatechuic acid
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