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Sodium Triacetoxyborohydride (STB) is a white powder with the chemical formula NaBH(OAc)₃, and its molecular weight is about 252.06 g/mol. It is solid at room temperature. It is usually in the form of needle-like crystals or massive crystals, and is relatively light and easy to handle. It is slightly soluble in water, and has good solubility in polar solvents such as absolute ethanol, methanol, dimethyl sulfoxide and chloroform, and is a mild and selective borohydride reagent. This allows the compound to be soluble in most commonly used solvents and to function in many chemical reactions. Stable to a certain extent, it can be stored for several months to several years at room temperature, and will not be easily decomposed. However, the compound is prone to decomposition under extreme conditions such as high temperature or high humidity, so it must be preserved properly to ensure its quality. The compound is stable and easy to store. These physical properties make it an important reducing agent and play an important role in organic synthesis. For the reductive amination of ketones and aldehydes, the reductive amination/lactoamylation of carbonyl complexes and amines, and the reductive amination of aryl aldehydes. The novel reductive amination catalyst has excellent universality and selectivity, mild reaction conditions, good catalytic reduction performance, easy separation and purification, the catalyst itself and by-products are non-toxic, and have no pollution to the environment. Has become the catalyst of choice for reductive amination reactions.
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Chemical Formula |
C6H10BNaO6 |
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Exact Mass |
212 |
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Molecular Weight |
212 |
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m/z |
212 (100.0%), 211 (24.8%), 213 (6.5%), 212 (1.6%), 214 (1.2%) |
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Elemental Analysis |
C, 34.00; H, 4.76; B, 5.10; Na, 10.85; O, 45.29 |
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Sodium Triacetoxyborohydride (CAS number 56553-60-7) is an important organic boron compound. As a derivative of sodium borohydride, its unique chemical properties make it occupy a core position in the field of organic synthesis. Its molecular formula is C ₆ H ₁₀ BNaO ₆, with a molecular weight of 211.94 g/mol. It appears as a white crystalline powder and is easily soluble in organic solvents such as benzene, tetrahydrofuran (THF), acetonitrile (MeCN), and 1,2-dichloroethane (ClCH ₂ CH ₂ Cl). However, it reacts with water to produce hydrogen gas and acetate salts, and needs to be used in the absence of water.
1. Reduction amination reaction
Reduction amination is a key reaction that converts carbonyl compounds (aldehydes, ketones) into amine compounds, and its process is divided into two steps:
Imine formation: Carbonyl compounds react with amines (primary or secondary) under weakly acidic conditions (such as acetic acid catalysis) to form imines (Schiff bases).
Imine reduction: As a reducing agent, selectively reduce imine to amine while avoiding carbonyl reduction.
Reaction advantage:
Mild conditions: No high pressure or extreme temperature is required, it can be completed from room temperature to 60 ℃, and weak acidic conditions (pH 4-6) can avoid excessive protonation of amines leading to decreased nucleophilicity.
Functional group compatibility: It has no effect on sensitive groups such as carbon carbon double bonds, nitro groups, and cyano groups, and is superior to platinum/palladium catalytic hydrogenation method (the latter is prone to mixture formation and has low yield).
Solvent optimization: When using 1,2-dichloroethane as the solvent, the reaction rate is the fastest and the yield is significantly improved; THF and MeCN can also be used, but with slightly lower efficiency.
Typical case:
Aromatic aldehyde reduction amination: benzaldehyde and aniline are catalyzed by acetic acid to form imine, which is then reduced to obtain N-benzylaniline in high yield for the synthesis of antidepressants.
Complex drug molecule synthesis: In the synthesis of anticancer drug imatinib, precise introduction of amino groups through reductive amination reaction ensures molecular activity and structural integrity.
2. Reduction of carbonyl complexes
Selective reduction of carbonyl groups in carbonyl complexes (such as ketones and aldehydes) to generate alcohol compounds while retaining other functional groups.
Reaction characteristics:
Selective control: By adjusting reaction conditions such as solvent and temperature, selective reduction of carbonyl and carbon carbon double bonds can be achieved. For example, in compounds containing alpha, beta unsaturated ketones, the carbonyl group is preferentially reduced without affecting the double bond.
Catalytic amount of acetic acid assistance: For ketone substrates, adding catalytic amount of acetic acid can accelerate the reaction, or it can be carried out directly in acetic acid.
Application example:
Endoamidation reaction: Reacting ketones with amines to produce lactams (cyclic amides), which are used in the synthesis of antibiotics such as penicillins.
Preparation of chiral alcohols: In the presence of chiral catalysts, sodium triacetoxyborohydrid can asymmetrically reduce aldehydes and ketones to generate chiral alcohols, which are used for the synthesis of chiral drugs (such as antiviral drug oseltamivir).
Special application scenarios: Green chemistry and asymmetric synthesis
1. Green chemistry substitution
As a substitute for sodium cyanoborohydride (NaBH ∝ CN), it has significant advantages:
Improved safety: No cyanide ions present, avoiding the risk of cyanide toxicity and complying with green chemistry principles.
No need for acid-base adjustment: NaBH ∝ CN needs to be used under strong acidic conditions (pH 2-3), while it can react efficiently under weak acidic conditions, simplifying the operation process.
Case comparison:
Limitations of NaBH ∝ CN: When reducing aromatic aldehydes, it is necessary to strictly control the pH value, otherwise it may lead to side reactions; Under pH 4-6 conditions, the reaction can be stabilized and the yield can be increased by 20% -30%.
Industrial application: A pharmaceutical company used sodium triacetoxyborohydride to synthesize anti allergic drugs, replacing NaBH ∝ CN, resulting in a 30% reduction in production cycle and a 50% reduction in waste.
2. Asymmetric synthesis
In the presence of chiral catalysts such as BINOL phosphates, aldehydes and ketones can be asymmetrically reduced to generate chiral alcohols, which can be used for the synthesis of chiral drugs or pesticides.
Reaction mechanism:
Chiral induction: Chiral catalysts guide hydrogen anions to selectively attack the Re or Si surface of carbonyl groups through hydrogen bonding or steric hindrance effects, achieving stereoselective reduction.
High enantioselectivity: Under optimized conditions, the enantiomer excess (ee) can reach over 95%, meeting the high purity requirements for drug synthesis.
Application example:
Antidepressant drug synthesis: The (S) - fluoxetine intermediate is synthesized through asymmetric reduction, with an ee value of 98%, avoiding the step of racemic separation and reducing costs.
Pesticide intermediate preparation: Synthesize chiral herbicide intermediates to enhance pesticide activity and reduce environmental residues.
Industrial application examples: pharmaceuticals and fine chemicals
1. Pharmaceutical field
Synthesis of anticancer drugs: In the synthesis of imatinib, amine groups are introduced through reductive amination reactions, and the high selectivity of sodium triacetoxyborohydrid avoids side reactions, improving product purity to over 99.5%.
Preparation of antiviral drugs: When synthesizing intermediate oseltamivir, asymmetric reduction is used to generate chiral alcohols with an ee value of 98%, which meets the international pharmacopoeia standards.
2. Fine chemical industry field
Spice synthesis: Reduce aldehyde spice raw materials to alcohols to enhance aroma persistence. For example, vanillin is reduced to vanillin for the synthesis of high-grade perfume.
Preparation of intermediate materials: When synthesizing polyimide monomers, amine groups are introduced through reductive amination reaction to improve the heat resistance of the material.
Sodium triacetoxyborohydride is a novel catalyst specifically designed for reductive amination reactions and is highly favored due to its unique advantages. It has extremely high universality and selectivity, can catalyze reactions gently, and exhibits good reduction performance. In addition, its separation and purification process is simple, and the catalyst itself and by-products are non-toxic, making it an ideal catalyst for reductive amination reactions and environmentally friendly.
Although metal catalyzed hydrogenation such as platinum, palladium, or nickel is economical and effective in large-scale production, their products are usually mixtures with low yields. This method still has limitations as it cannot handle compounds containing carbon carbon bonds and reducible functional groups such as nitro and cyano groups, as their catalytic performance is inhibited by divalent sulfides.
The core of the reductive amination reaction is to convert carbonyl compounds into amines by first forming imines and then reducing them using sodium borohydride (including STB). Different types of sodium borohydride have similar reduction steps after forming imines, mainly reducing imines to amines. This process is carried out under weakly acidic conditions to enhance the electrophilicity of carbonyl groups while avoiding the decrease in nucleophilicity caused by excessive protonation of amines.
The use of sodium cyanoborohydride for reduction is superior to sodium borohydride because the electrostatic induction effect of the cyanide group reduces the activity of boron hydrogen bonds, ensuring selective reduction of only selegiline and avoiding non targeted reduction of aldehydes and ketone carbonyl groups, thereby reducing the occurrence of side reactions. By using NaBH (OAc) 3 as a reducing agent and ClCH2CH2Cl as a solvent, the reaction time can be effectively shortened and the yield of the product can be improved.
Sodium Triacetoxyborohydrid is a kind of organic synthesis reagent, which is widely used in reactions such as reduction, condensation and synthesis of heterocyclic compounds. It is usually synthesized by several methods, all of which will be described in detail.
1. Cyclic tetraphenylphosphine salt method:
The cyclic tetraphenylphosphonium salt method is one of the main methods for preparing product. In the method, triphenylphosphine and triacetoxyborontriethyl ester are used as raw materials, and a reduction reaction occurs in the presence of tributylaluminum hydride and hydroxyethyltriphenylphosphine to generate it.
The reaction equation is as follows:
B(OAc)3 + 3Ph3P + 3EtOH → NaBH(OAc)3 + 3Ph3PO + 3EtOAc
The synthesis method has the advantages of high yield, mild reaction conditions and easy operation. However, due to the high price of raw materials, the production cost is relatively high.
2. Boric acid and ethyl iodide method:
The method of boric acid and ethyl iodide is a convenient synthesis method, and it is also one of the commonly used methods for preparing Sodium Triacetylborohydride. The method is based on the alkylophilicity of ethyl iodide, directly reacts boric acid and ethyl iodide to generate triiodoethyl borate, and then obtains Sodium Triacetylborohydride through the reduction reaction of sodium.
The reaction equation is as follows:
H3BO3 + 3I(C2H5) → B(I(C2H5))3 + 3H2O
B(I(C2H5))3 + 3NaH → NaBH(OAc)3 + 3C2H5I
The synthesis method has the advantages of simple operation and no need for special reaction conditions, but the product has low purity and needs to be further purified through steps such as recrystallization or column chromatography.
In conclusion, it is an important organic synthesis reagent with broad application prospects. It can be synthesized by various methods. Each method has its specific advantages and disadvantages, so in the actual production process, it is necessary to choose the appropriate method according to the specific situation.
Sodium Triacetoxyborohydride is a colorless, crystalline solid with the chemical formula NaBH(OAc)3, where BH(OAc)3 stands for triacetoxyborohydride. Its molecular weight is about 252.4 g/mol. At room temperature, it has high thermal and chemical stability, and can be stored and used under normal experimental conditions.
1. Molecular structure:
The molecular structure of it is composed of three acetoxy groups and a borohydride ion. The structure of the borohydride ion is similar to a regular tetrahedron, in which the B atom is located at the center, and three OAc groups are distributed equidistantly and equiangularly around it, and each H atom is connected to an OAc group to form a bond with the B atom. In addition to borohydride ions, sodium ions also play an important role in structure stabilization in the lattice.
2. Crystal structure:
The crystal structure of Sodium Triacetylborohydride was obtained in 1973 by G. W. Parshall et al. It is monoclinic with space group P21/c. The unit cell parameters are a = 13.236 Å, b = 16.145 Å, c = 9.048 Å, and β = 96.74°. The unit cell contains four molecules, each of which interacts with other molecules through hydrogen bonds, forming a three-dimensional network structure. In the lattice, the borohydride ion forms hydrogen bonds with three different OAc groups through H atoms, making the distance between them about 1.2 Å. The sodium ion forms an ionic bond with one of the three OAc groups.
The following is a brief introduction about the main chemical properties of the compound:
1. Reducibility:
Sodium Triacetylborohydride is a strong reducing agent that can reduce many organic compounds to lower oxidation states. For compounds containing oxygen functional groups, such as aldehydes, ketones, acids and esters, it will usually be selectively reduced to the corresponding alcohols or hydroxyl compounds. For compounds containing sulfur functional groups, such as mercaptans and disulfides, the reducing agent also has strong reducing properties.
3. Stability:
Although STB is a strong reducing agent, it is more stable than other commonly used reducing agents such as sodium borohydride. During storage and use, the compound is not easily affected by conditions such as air, moisture and temperature. At the same time, it should also be noted that it should avoid contact with oxidizing agents, such as hydrogen peroxide or potassium permanganate, otherwise dangerous reactions will occur.
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