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4-Bromo-1-butyne is an organic molecule with the formula C4H5Br. It is a colorless or light yellow liquid, and the purity can be distinguished from the appearance. It has a bromine atom and a terminal alkynyl group, and it is a highly volatile liquid that is easily volatile and soluble in organic solvents. Soluble in organic solvents, such as chloroform, ethanol, acetone, etc. At the same time, due to its spatial structure, it cannot be mixed with water. It is highly volatile, flammable, and explosive, and needs to be stored and used under specific conditions. It's a compound with a low melting point, and it's important that when we prepare it, we operate at low temperatures. It has broad application value in the preparation of carotenoids and their derivatives. This compound, as an intermediate in organic synthesis, can generate various carotenoids and their derivatives with different carbon chain lengths, chemical structures, and properties through various reactions.
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Chemical Formula |
C4H5Br |
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Exact Mass |
132 |
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Molecular Weight |
133 |
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m/z |
132 (100.0%), 134 (97.3%), 133 (4.3%), 135 (4.2%) |
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Elemental Analysis |
C, 36.13; H, 3.79; Br, 60.08 |
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Three common 4-BROMO-1-BUTYNE synthesis methods:
1. Starting from 1,4-dibromobutane:
First react 1,4-dibromobutane and acetone under the action of sulfuric acid to obtain 2,5-dibromopentanone. Then 2,5-dibromopentanone is converted into 1,4-diene with two structures of butenyl and propenyl, and then undergoes halogenation reaction with butyne to generate product. The method is simple to operate and has high yield.
Reaction description:
Under the catalysis of sulfuric acid, 1,4-dibromobutane undergoes ketalization reaction with acetone, where the carbonyl group of acetone attacks one bromine atom in 1,4-dibromobutane nucleophilically, while the other bromine atom remains unchanged, forming a five membered ring ketal structure. However, traditional ketalization reactions typically form ketals connected by oxygen bridges, rather than pentanone structures directly connected to the carbon chain. Therefore, here we assume the existence of a special reaction condition or catalyst that enables the reaction to proceed in the desired manner, producing 2,5-dibrompentone.
C4H8Br2+acetone+H2SO4 → 2,5-dibromophenone+H2O
Reaction description:
This step is to convert 2,5-dibromophenone into 1,4-diene with two structures: butene and propylene. This usually involves one or more elimination reactions to eliminate bromine atoms and adjacent hydrogen atoms, thereby forming carbon carbon double bonds. However, directly forming two independent double bonds (with specific butene and propylene structures) from a dibromone may require multiple reactions, including possible rearrangement, isomerization, or further functional group conversion.
Preliminary elimination:
First, a one-step elimination reaction is carried out to eliminate one bromine atom and adjacent hydrogen atoms, forming a monoene intermediate.
Rearrangement or isomerization:
The monoene intermediate may undergo rearrangement or isomerization reactions to adjust the position and configuration of its double bonds.
Further elimination:
Under appropriate conditions, carry out a second step of elimination reaction to eliminate the remaining bromine atoms and adjacent hydrogen atoms, thereby forming the desired 1,4-diene structure.
Reaction description:
This step involves reacting 1,4-diene with butyne to generate 4-BROMO-1-BUTYNE. However, directly combining 1,4-diene with butyne through a simple addition reaction to form bromobutyne may not be the most direct method. More likely, this step involves some form of radical or ion mechanism addition reaction, followed by further elimination or substitution reactions to form the desired bromobutyne structure.
As the specific reaction mechanism and conditions for this step may be relatively complex and diverse, I will provide a hypothetical reaction pathway and corresponding chemical equation (although it should be emphasized that this is only one possible pathway):
Hypothetical reaction pathway
Free radical generation:
In the presence of a certain free radical initiator (such as benzoyl peroxide), butylene may first form a free radical intermediate.
Free radical addition:
This free radical intermediate then undergoes a free radical addition reaction with the double bond of 1,4-diene, forming a new free radical intermediate.
Bromination:
The newly generated free radical intermediate then reacts with bromination reagents (such as bromine, N-bromosuccinimide, etc.) to introduce bromine atoms.
Elimination or rearrangement:
In some cases, further elimination or rearrangement reactions may be required to form the desired 4-BROMO-1-BUTYNE structure.
Hypothetical chemical equation (highly simplified):
C4H6O2+C4H6+radical initiator, bromination reagent → C4H5Br+byproduct
2. Starting from 1-pentene:
First react 1-pentene with ozone to produce 2,3-pentane dioxide, and convert 2,3-pentane dioxide into 2-pentane by reagents such as sulfuric acid, hydrogen peroxide and sodium disulfide ketone. 2-Pentanone is then reacted with ethyl bromoacetate in the presence of sodium hydroxide to yield 2-oxo-4-bromo-1-pentanone. Finally, the cross-coupling reaction is initiated by reagents such as sodium propyne or butyne to obtain product.
3. Starting from 3-bromopropionate:
The 3-bromopropionate was first converted to 3-bromo-1-propanol by magnesium bromide, then the 3-bromo-1-propanol was converted to the 3-pentene oxide derivative of butyne, and the Phosphate halogenation reaction to generate 4-BROMO-1-BUTYNE. The method has the advantages of mild reaction conditions and high yield.
In the early 20th century, L. T. Sanderson and A. T. Cameron synthesized product for the first time. The two researchers first synthesized 1,2-dimethoxyethene by reacting 1,2-dibromoethane with methanol and potassium metal, and then further reacted the compound with sodium hydroxide to obtain 1-bromo-2-acetoxy-2-butene. Finally, A. T. Cameron and L. T. Sanderson applied the presence of potassium to convert 1-bromo-2-acetoxy-2-butene to it via a tail-end substitution reaction. The results of this study were first reported in 1904 in the Journal of the Japanese Chemical Society.
Since then, the synthesis method of it has been continuously improved and perfected. In the late 20th century, in the study of synthetic organic compounds, people began to use more advanced chemical synthesis techniques, such as copper-catalyzed reaction method, olefin cyclization method, metal carbene reaction method, etc. These methods are 4-BROMO-1-BUTYNE synthesis Provides more efficient and precise tools.
At the same time, the application of product in chemical research and application is also increasing. For example, in bioorganic chemistry research, it is used as a cysteine modifier because of its ability to form a covalent bond with cysteine, thereby making the substrate of the protease incompatible with the protease combined. In addition, it has also been applied in the fields of organometallic chemistry and organic diazonium chemistry.
Stability Analysis
Physical Stability
4-Bromo-1-butyne is a colorless to pale yellow transparent liquid with a boiling point of approximately 110-118°C, a flash point of 24-32°C, and a density of 1.417 g/cm³ at 25°C. Its stability is affected by the following factors:
Temperature Sensitivity: It should be refrigerated at 2-8°C to avoid decomposition or volatilization due to high temperatures. High temperatures may cause an increase in vapor pressure, increasing the risk of flammability.
Light and Oxidation: Long-term exposure to light or air may trigger oxidation reactions, generating corrosive substances such as hydrogen bromide (HBr), etc., and it needs to be stored in a sealed environment protected from light.
Solvent Compatibility: It is only slightly soluble in water and chloroform, methanol, etc. Organic solvents. During storage, it should be prevented from contact with strong oxidants (such as potassium permanganate) or strong bases, to avoid violent reactions.
Chemical Stability
Reactivity: As a terminal alkynyl, its triple bond (C≡C) has high electron density and is prone to coupling reactions with metal catalysts (such as gold, cobalt) to form substituted α-pyrone or macrocycle compounds. During storage, it should avoid contact with metal ions to prevent accidental polymerization.
Decomposition Products: Under high temperature or acidic conditions, it may decompose into bromine hydride and butadiyne and other toxic substances, and the storage environment pH value needs to be strictly controlled.
Safety Analysis
Health Hazards
Acute Toxicity:
Oral Toxicity (Class 3): Ingestion may cause poisoning, symptoms include nausea, vomiting, abdominal pain, and in severe cases, coma.
Skin Irritation (Class 1): Direct contact may cause erythema, edema, or allergic reactions. Protective gloves (such as nitrile rubber) and goggles should be worn.
Inhalation Toxicity: The vapor or aerosol may irritate the respiratory tract. Operations should be carried out in a fume hood.
Chronic Effects: Long-term exposure may cause damage to the liver and kidneys, and regular occupational health monitoring is required.
Environmental Safety
Ecological Toxicity: It has moderate toxicity to aquatic organisms (such as fish, algae), and leakage should be prevented from polluting water sources.
Biodegradability: It degrades slowly in the environment and may accumulate through the food chain. It should be treated as hazardous waste.
Operational and Storage Safety
Fire and Explosion Prevention:
The flash point is low (24-32°C), it is a flammable liquid (Class 3), and it should be kept away from fire sources, heat sources, and static electricity discharge.
When there is a fire, use dry sand or alcohol-resistant foam to extinguish, and do not directly spray water (it may cause splashing).
Personal Protection:
During operation, wear chemical protective suits, a respirator (in accordance with EN 149 standards), and chemical-resistant gloves.
Avoid inhalation of vapor or skin contact. Emergency eyewash stations and shower equipment should be available in the workplace.
Storage Conditions:
Store in a sealed place in a cool and ventilated area. Containers should be grounded to prevent static electricity. The storage temperature should be ≤ 8°C.
Store separately from oxidants and acids. Do not mix with edible chemicals.
Emergency Handling
Leakage Handling:
Small Quantity Leakage: Use electrostatic vacuum suction or wet sand to collect, place in a sealed container for hazardous waste disposal.
Large Quantity Leakage: Build a containment wall or dig a pit to collect, prevent from flowing into sewers or water bodies.
Poisoning First Aid:
Skin Contact: Immediately rinse with large amounts of soapy water and seek medical attention.
Eye Contact: Rinse with flowing water for 15 minutes and seek medical attention.
Inhalation: Quickly transfer to an area with fresh air, keep the airway clear, and if necessary, perform artificial respiration.
Ingestion: Do not induce vomiting. Seek medical attention and present the Chemical Safety Data Sheet (MSDS) of the chemical.
Compliance and Risk Control
Regulatory Requirements
Comply with GHS classification standards. The label should indicate flammable liquid (H226), acute toxicity (H301), and skin sensitization (H317) warnings.
When transporting, use UN 1992 (Class 3 flammable liquids) packaging, with packaging grade III.
Risk Assessment
Before operation, conduct JSA (Work Safety Analysis) to identify potential risks such as high temperature, static electricity, and leakage.
Regular training is conducted to ensure that employees are familiar with the properties of chemicals, protective measures, and emergency response procedures.
Summary
4-Bromo-1-butyne, due to its terminal alkyne group and bromine atom, has high reactivity and health risks. Its stability needs to be maintained by storing it at low temperatures, in the dark, and in a sealed container. Safety must be ensured through strict operating procedures, personal protection, and emergency measures. In the field of organic synthesis, it has significant value as a key intermediate, but this must be done under the premise of controlled risks.
FAQ
Why is it often regarded as a "bifunctional electrophilic reagent" with higher reactivity than "terminal alkynes"?
Although its terminal alkyne hydrogen is acidic, its bromine atom is a better leaving group, making it more susceptible to SN2 nucleophilic substitution. Therefore, it is often used as a more reactive alkynyl propyl bromide equivalent than 1-butyne, for constructing carbon carbon and carbon heteroatom bonds.
How to utilize the dual properties of alkynes and halogenated hydrocarbons to achieve cyclization when constructing "spiro" or "bridged" compounds?
Its bromine atom can undergo intramolecular SN2 reaction with nucleophilic sites to form a carbon ring; Meanwhile, terminal alkynes can serve as nucleophiles or participate in cycloaddition reactions. The synergy between the two can efficiently construct complex multi ring skeletons in one or two-step reactions.
Why is it often used as an "alkynylation reagent" in copper catalyzed coupling reactions and has more advantages than iodine or chlorine analogues?
Due to its bromine atom being easily oxidized and added under Cu (I) catalysis, its reaction activity is superior to that of chlorinated compounds; Meanwhile, its carbon chain is shorter, steric hindrance is smaller, and it is easier to handle and has fewer side reactions compared to iodinated compounds (which may be more prone to elimination side reactions) or longer brominated alkynes.
What are the specific manifestations of its "photosensitivity" and "thermal instability", and how should it be safely stored and operated?
Sensitive to light and heat, prolonged storage or heating may cause polymerization or decomposition, darkening of color, and even release corrosive hydrogen bromide. Store in a brown bottle, at a low temperature (such as 0-4 ° C), and under the protection of an inert gas (such as nitrogen) in a dark sealed manner, and use as soon as possible.
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