5-Bromo-1-pentanol: Handling, Storage & Synthesis Protocol

5-Bromo-1-pentanol is a bifunctional ω-bromoalcohol widely used as a versatile synthetic intermediate in organic and medicinal chemistry, enabling selective transformations at either the hydroxyl or the terminal bromide functional group.

CAS Number

5798-75-4

Molecular Formula

C₅H₁₁BrO

Molecular Weight

167.04 g/mol

Appearance

Colorless to pale yellow liquid

Key Functional Groups

Terminal alkyl bromide (C5) and primary alcohol (C1)

Recommended Storage

Cool, dry, well-ventilated area; sealed container away from light

Primary Applications

Alkylating agent, ring-closure precursor, linker in bioconjugation

Overview and Chemical Properties

5-Bromo-1-pentanol (CAS 5798-75-4) is a bifunctional five-carbon building block bearing a primary hydroxyl group at C1 and a terminal alkyl bromide at C5. This combination of complementary reactive sites makes it exceptionally useful in multi-step organic synthesis, where each group can be independently protected, activated, or coupled depending on the synthetic strategy.

The compound is a liquid at room temperature and is miscible with common organic solvents such as dichloromethane, tetrahydrofuran, ethyl acetate, and acetone, while exhibiting limited miscibility with water. Its moderate molecular weight (167.04 g/mol) and relatively low volatility compared to short-chain bromoalcohols facilitate safe handling under standard laboratory fume-hood conditions.

The C–Br bond at the terminal position confers good electrophilic reactivity toward nucleophiles (e.g., amines, thiols, alkoxides, malonates), while the primary hydroxyl group can be oxidized, esterified, etherified, or converted to other leaving groups. This orthogonal reactivity profile is the principal reason 5-Bromo-1-pentanol is routinely employed as a tether or linker molecule in target-oriented synthesis.

Safety, PPE, and Handling Precautions

Personal Protective Equipment (PPE): Always wear nitrile or neoprene gloves, a laboratory coat, and chemical-splash safety goggles when handling 5-Bromo-1-pentanol. Perform all weighing, transfers, and reactions in a well-ventilated fume hood to minimize inhalation exposure.

Skin and eye contact: The compound is an irritant. In the event of skin contact, remove contaminated clothing and wash the affected area thoroughly with soap and water for at least 15 minutes. For eye contact, irrigate with large amounts of water for at least 15 minutes and seek medical attention. Do not induce vomiting if ingested; seek medical attention immediately.

Fire and reactivity hazards: 5-Bromo-1-pentanol is a combustible liquid. Keep away from open flames, sparks, and strong oxidizing agents. Store separately from strong bases and reducing agents.

Waste disposal: Dispose of waste material in accordance with local, regional, and national regulations for halogenated organic solvents. Do not pour down the drain.

Spill management: Absorb small spills with inert material (e.g., vermiculite or dry sand), collect in a sealed container, and label for disposal. Ventilate the area thoroughly.

Standard Laboratory Protocol: Nucleophilic Alkylation Using 5-Bromo-1-pentanol

The following general protocol describes the use of 5-Bromo-1-pentanol as an alkylating agent in a nucleophilic substitution reaction (S_N2) with a nucleophile such as a sodium alkoxide, amine, or thiolate salt. Adapt reagent quantities and conditions to your specific system.

Materials required:

• 5-Bromo-1-pentanol (1.0 equiv, Aladdin Scientific SKU B135090)
• Nucleophile (1.0–1.5 equiv; e.g., NaOH-generated alkoxide, primary amine, or sodium thiolate)
• Anhydrous polar aprotic solvent (DMF, DMSO, or acetonitrile; dried over molecular sieves)
• Base if required (K₂CO₃, Cs₂CO₃, or Et₃N; 1.5–2.0 equiv)
• Magnetic stir bar, round-bottom flask, reflux condenser, nitrogen/argon inlet
• Thin-layer chromatography (TLC) supplies for reaction monitoring

Procedure:

1. Setup: Flame-dry a round-bottom flask, cool under inert atmosphere (N₂ or Ar), and add the nucleophile and base (if used) in anhydrous solvent (0.1–0.5 M).
2. Addition: Add 5-Bromo-1-pentanol (neat or as a solution in the same solvent) dropwise via syringe at room temperature or 0 °C.
3. Reaction: Stir the mixture at the appropriate temperature (typically 50–80 °C for sluggish nucleophiles; room temperature for reactive ones) until TLC or GC-MS indicates complete consumption of the bromide starting material (typically 2–12 hours).
4. Work-up: Cool to room temperature, dilute with ethyl acetate or diethyl ether, wash sequentially with water and brine, dry over anhydrous MgSO₄ or Na₂SO₄, and filter.
5. Purification: Remove solvent under reduced pressure and purify by silica gel column chromatography or recrystallization as appropriate.
6. Analysis: Confirm product identity by ¹H NMR, ¹³C NMR, and high-resolution mass spectrometry (HRMS).

Note: When selective reaction at only one functional group is desired, protect the hydroxyl group as a silyl ether (e.g., TBS or TMS) or the bromide may be converted to a different leaving group prior to nucleophilic displacement.

Storage, Stability, and Quality Control

Storage conditions: Store 5-Bromo-1-pentanol in a tightly sealed amber glass bottle in a cool (2–8 °C recommended for long-term storage), dry, and well-ventilated area, away from light, heat sources, and incompatible materials. Avoid prolonged exposure to air and moisture, which may promote slow hydrolysis of the C–Br bond or oxidation of the alcohol.

Shelf life and stability: Under recommended storage conditions, 5-Bromo-1-pentanol is stable for an extended period. However, because terminal alkyl bromides can undergo slow elimination or solvolysis, periodic quality checks are recommended for reagents stored beyond 12 months. Discard if the liquid appears discolored (dark brown or contains visible precipitate).

Quality control checks before use:

• Visual inspection: The reagent should be a clear, colorless to pale yellow liquid. Significant darkening suggests decomposition.
• GC purity: Check purity by gas chromatography (GC) against a reference standard. Acceptable purity is typically ≥95% by GC.
• ¹H NMR fingerprint: Key signals include a triplet at δ ~3.40 ppm (–CH₂Br), a triplet at δ ~3.63 ppm (–CH₂OH), and multiplets for the internal methylene protons (δ ~1.50–1.90 ppm).

Incompatibilities: Strong oxidizing agents, strong bases, strong acids, moisture, and reducing agents.

Common Applications in Organic and Medicinal Chemistry

5-Bromo-1-pentanol occupies a central role in synthetic chemistry due to its dual reactivity and the favorable five-carbon tether length. Key applications include:

• Ether synthesis: The terminal bromide undergoes S_N2 reaction with alkoxides to form ω-hydroxy ethers, which are useful intermediates in natural product synthesis.
• N-Alkylation: Amines (primary or secondary) react with the C–Br terminus under mild basic conditions to yield N-(5-hydroxypentyl) derivatives used in drug design and amino acid modification.
• Cyclic ether (tetrahydropyran) formation: Under acidic conditions or with appropriate activation, 5-Bromo-1-pentanol can undergo intramolecular cyclization to form tetrahydropyran (THP), a six-membered cyclic ether.
• Macrocyclization and ring-closing metathesis precursors: The bifunctional nature allows it to serve as a chain extender in the synthesis of macrocyclic lactones, lactams, or crown ethers.
• Bioconjugation linkers: The compound is used to introduce pentyl spacers bearing a hydroxyl handle for attachment to solid supports or biomolecule coupling.
• Polymer and materials chemistry: Employed as a chain-end functional group modifier in controlled radical polymerizations (e.g., ATRP, RAFT) to install hydroxyl-terminated chains.

In all cases, careful selection of reaction conditions ensures chemoselectivity between the two functional groups.

Frequently asked questions

Can 5-Bromo-1-pentanol be used directly as a solvent or does it require dilution?

5-Bromo-1-pentanol is a reagent, not a solvent. It should always be used in diluted form in an appropriate anhydrous polar aprotic solvent (such as DMF, DMSO, or acetonitrile) at a concentration suited to the reaction scale. Using it neat is only appropriate when it serves simultaneously as both reagent and reaction partner in excess.

How do I selectively react the bromide terminus without affecting the hydroxyl group?

To achieve chemoselectivity at the C–Br terminus, protect the primary hydroxyl group as a silyl ether (e.g., TBS-Cl, imidazole in DMF) before performing the nucleophilic substitution. After the desired C–Br reaction is complete, the silyl protecting group can be removed under mild fluoride (e.g., TBAF in THF) or acidic conditions. Alternatively, mild nucleophiles that do not react with primary alcohols can sometimes be used without protection.

What is the best base to use for N-alkylation of an amine with 5-Bromo-1-pentanol?

For N-alkylation, mild inorganic bases such as potassium carbonate (K₂CO₃) or cesium carbonate (Cs₂CO₃) in DMF or acetonitrile at 50–80 °C are commonly effective. These bases neutralize the HBr generated in situ without causing elimination side reactions. For more hindered or less reactive amines, stronger bases or elevated temperatures may be required; consult the specific literature for your substrate.

What is the typical reaction temperature for intramolecular cyclization of 5-Bromo-1-pentanol to tetrahydropyran?

Intramolecular cyclization to form tetrahydropyran typically proceeds under acidic conditions or basic conditions (e.g., using NaOH or K₂CO₃ in aqueous or mixed solvent systems). Exact temperatures vary with the reaction conditions; mild conditions (room temperature to 60 °C) are often sufficient given the favorable six-membered ring transition state. Consult primary literature for your specific conditions and yield data.

How should I dispose of waste containing 5-Bromo-1-pentanol?

Waste containing 5-Bromo-1-pentanol must be classified and disposed of as halogenated organic waste in accordance with your institution's chemical waste management procedures and applicable local and national regulations. Do not pour it down the drain or mix it with non-halogenated waste streams. Label all waste containers clearly with the chemical name and hazard information.

References

1. March, J.; Smith, M. B. March's Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, 7th ed.; Wiley: Hoboken, NJ, 2013.
2. Clayden, J.; Greeves, N.; Warren, S. Organic Chemistry, 2nd ed.; Oxford University Press: Oxford, 2012.
3. Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic Synthesis, 4th ed.; Wiley-Interscience: New York, 2006.
4. Sigma-Aldrich / Merck product entry for 5-Bromo-1-pentanol. Safety Data Sheet. [Online resource; access date variable].

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