RU2072980C1 - Method of separation of vanillin and syringaldehyde - Google Patents

Abstract

FIELD: chemical technology, organic synthesis. SUBSTANCE: invention relates to the synthesis of vanillin (4-hydroxy-3-methoxybenzaldehyde) and syringaldehyde (4-hydroxy-3,5-dimethoxybenzaldehyde). Vanillin and syringaldehyde were separated by mixture dissolving in potash solution (100-400 g/l) at 60-100 C and potassium syringate is precipitated at 20-40 C and potassium vanillate - at 0-20 C. The obtained precipitate of syringate and vanillate is dissolved in water and vanillin and syringaldehyde were precipitated by acidification with carbon dioxide gas. Yield of vanillin and syringaldehyde is up to 96% of initial and content of the second component is less 0.5%. Potash and carbon dioxide gas were regenerated from the potassium hydrocarbonate solutions by heating up to 80-100 C. EFFECT: excluding toxic methanol, ammonia, improved separation of products without reagent consumption.

Description

 The claimed invention relates to the field of fine organic synthesis and is intended to improve the processes for the joint production of vanillin (4-hydroxy-3-methoxybenzaldehyde) and lilac aldehyde (4-hydroxy-3,5-dimethoxybenzaldehyde) from lignin-containing raw materials. The resulting products are used in the food, perfumery, cosmetic and pharmaceutical industries.

 It is well known that the oxidation of hardwood lignins produces a mixture of vanillin (B) and lilac aldehyde (CA). The allocation of the mixture of aldehydes is carried out by extraction, followed by purification of B and CA through sodium bisulfate derivatives.

A known method of separation of B and CA selective extraction at a fixed pH [1,2] The disadvantage of this method is its high complexity and complexity. Due to the proximity of the acidity of aldehydes (pK _a ), this process requires dozens of countercurrent extraction stripping steps [2]
A known method of separating B and CA by precipitating the complex of the latter with ammonia from aqueous methanol solution [3] For the process, the mixture of aldehydes is dissolved in 30-90% aqueous methanol to a concentration of 50-300 g / l, then ammonia is added to the solution gaseous form or in an aqueous / aqueous methanol solution, while the complex of lilac aldehyde with ammonia precipitates, and vanillin remains in solution. This process is apparently caused by the formation of lilac aldehyde and ammonia hydrobenzamide, which is not formed from more acidic vanillin. The less acid lilac aldehyde in the ammonia solution is much less dissociated, as a result of which it reacts with ammonia and is removed from the reaction sphere. The precipitate formed is separated by centrifugation. The regeneration of aldehydes is carried out by adding to the ammonia solution of vanillin or to a suspension of a complex of lilac aldehyde with ammonia a strong mineral acid. After acidification, the precipitation of vanillin from a water-methanol solution is carried out by distillation of methanol to crystallize vanillin. Method [3] we have chosen as a prototype.

 The main disadvantage of the prototype is the use of toxic methanol, as well as the difficulty of regenerating ammonia after the process.

 The aim of the present invention is to remedy these disadvantages of the prototype: the exclusion of methanol and ammonia from the separation process.

The goal is achieved by sequential precipitation of syringate and potassium vanillate from aqueous solutions containing 100-400 g / l potash K ₂ CO ₃ . We unexpectedly found that the solubilities of syringate and potassium vanillate in concentrated potash solutions vary greatly and are characterized by a sharp temperature dependence. As a result, it is possible to separate B and CA as follows.

In an aqueous solution containing 100-400 g / l of potash, at a temperature of 60-100 ^o C, a mixture of B and CA is dissolved in an amount of 50-200 g / l. The solution is cooled to 20-40 ^o C, while a precipitate of less soluble potassium syringate is formed. The precipitate is separated, suctioned off and washed with a small amount of potash solution. The filtrate after separation of potassium syringate is cooled to 0-10 ^o C, while a precipitate of potassium vanillate is formed. The precipitate is separated, and the remaining potassium carbonate and potassium bicarbonate solution is heated to 60-100 ^{° C.} to decompose the bicarbonate ion and remove CO ₂ . A potassium carbonate solution is used to repeat the separation cycle, and carbon dioxide is used to isolate B and CA from phenolates.

The precipitated precipitates of vanillate and potassium syringate are dissolved in water and acidified with carbon dioxide. Precipitated precipitates of vanillate and lilac aldehyde are washed with water and, if necessary, subjected to further purification. The remaining potassium bicarbonate solution is heated to 60-100 ^o With to regenerate potash and remove carbon dioxide, which can be reused in the separation cycle.

KB_aq+CO₂+H₂O__→ HB↓_тв.+KHCO₃
KCA_aq+CO₂+H₂O__→ HCA↓_тв.+KHCO₃

где НВ, НСА нейтральные В и СА соответственно, а КВ, КСА ванилат и сирингат калия.Thus obtained B and CA contains more than 98-99% of the basic substance. It should be specially noted that the claimed method for the separation of vanillin and lilac aldehyde does not require stoichiometric consumption of reagents, but uses only thermal energy as the driving force of the processes:

KB _aq + CO ₂ + H ₂ O__ → HB ↓ _TV. + KHCO ₃
KCA _aq + CO ₂ + H ₂ O__ → HCA ↓ _TV. + KHCO ₃

where HB, HCA are neutral B and CA, respectively, and KB, CSA are vanillate and potassium syringate.

 A common feature of the claimed invention and prototype is the use of the precipitation process of compounds B and CA for their separation. An essential distinguishing feature of the proposed method is the use of concentrated aqueous solutions of potash for separate precipitation of vanillate and potassium syringate at different temperatures. The mentioned distinguishing feature allows to achieve the claimed technical result: to exclude the use of methanol and ammonia and the problems of their regeneration in the process of separation of B and CA.

 Example 1. A mixture of vanillin and lilac aldehyde was obtained by a known method of oxidizing aspen wood powder with oxygen in an alkaline environment. Aldehydes were extracted and the resulting mixture was purified through sodium bisulfite derivatives.

15 g of a mixture of aldehydes containing 28% vanillin and 70% lilac aldehyde were dissolved at 60 ^{° C.} in 100 ml of an aqueous solution containing 250 g / l of potash. The solution was cooled with stirring to 20 ^{° C.} , the precipitated potassium syringate was filtered off, washed with two 20 ml portions of the original potash solution. The filtrate containing potassium vanillate was cooled to 5 ^{° C.} , the vanillate precipitate was separated and washed similarly to syringate. The filtrate (a solution of KHCO ₃ and K ₂ CO ₃ ) was heated to 80 ^o C, there was an active allocation of CO ₂ .

The precipitate of potassium syringate was dissolved in 50 ml of water and a stream of carbon dioxide was passed until the precipitation of lilac aldehyde ceased. The precipitate was filtered off, washed with water and dried. Received 9.8 g of lilac aldehyde (93% of the original) with a vanillin content (according to GLC) of less than 0.5%. Vanillin was similarly isolated from potassium vanillate. Received 3.5 g of vanillin (83% of the original). The impurity content of lilac aldehyde in vanilla is less than 0.7%
After separation of B and CA, the filtrate was heated to 100 ^{° C.} to convert potassium bicarbonate to potash. The resulting potash solutions were combined and evaporated to a concentration of K ₂ CO ₃ 250 g / L. The described separation cycle of B and CA was repeated. Received 10.1 g of CA (96% of the original) and 4.05 g of B (96% of the original).

Example 2. 10 g of a mixture of aldehydes (28% vanillin and 70% lilac aldehyde) was dissolved at 60 ^{° C.} in 100 ml of a 100 g / L potash solution. Isolation of syringate and vanillate, as well as phenols, was carried out as described in Example 1. Sodium syringate was isolated by cooling the solution to 20 ^{° C.} , vanillate was cooled at 0 ^° C.

 Received 1.9 g of vanillin (68% of the original) and 5.2 g of lilac aldehyde (74% of the original).

Example 3. 20 g of a mixture of B (28%) and CA (70%) were dissolved at 100 ^{° C.} in 100 ml of potash with a concentration of 400 g / l. The procedures for the isolation of vanillin and lilac aldehyde are described in example 1. Potassium syringate was precipitated at 40 ^o C, and sodium vanillate at 20 ^o C.

 Received 13.1 g of CA (93% of the original) and 4.9 g of B (87.5% of the original).

Claims (1)

The method of separation of vanillin and lilac aldehyde by dissolution and precipitation of their compounds, characterized in that the initial mixture of aldehydes is dissolved in an aqueous potash solution with a concentration of 100 to 400 g / l at 60 - 100 ^o C, the resulting solution is cooled to 20 70 ^o C and the resulting precipitate is isolated potassium syringate by filtration, the obtained filtrate is cooled to 0 - 20 ^° C and the resulting potassium vanillate precipitate is isolated by filtration, then the precipitates of potassium syringate and potassium vanillate are separately dissolved in water and carbon dioxide is passed to obtain, respectively but lilac aldehyde and vanillin after filtration, the resulting filtrate is heated to 60 - 100 ^o With getting potash.