Cyclopentadiene (C5H6) is a cyclic compound with five carbon atoms and a double bond. It is commonly used in organic synthesis and as a building block for various chemical reactions.
| IUPAC Name | Cyclopentadiene |
| Molecular Formula | C₅H₆ |
| CAS Number | 542-92-7 |
| Synonyms | Cyclopenta-1,3-diene; 1,3-Cyclopentadiene; 1,3-Cyclopentadiene dimer; Dicyclopentadiene; CPD |
| InChI | InChI=1S/C5H6/c1-2-4-5-3-1/h1-4H,5H2 |
Cyclopentadiene Properties
Cyclopentadiene Formula
The chemical formula of cyclopentadiene is C₅H₆. It consists of five carbon atoms and six hydrogen atoms. This formula represents the elemental composition of the compound, providing insight into its molecular structure and properties.
Cyclopentadiene Molar Mass
The molar mass of cyclopenta-1,3-diene is approximately 66.10 g/mol. Molar mass is the mass of one mole of a substance and is calculated by summing the atomic masses of all the atoms in the formula. In the case of cyclopenta-1,3-diene, the molar mass is derived from the atomic masses of carbon and hydrogen.
Cyclopentadiene Boiling Point
Cyclopenta-1,3-diene has a boiling point of approximately 41.5 °C. The boiling point is the temperature at which a substance changes from its liquid phase to a gaseous phase under standard atmospheric pressure. The relatively low boiling point of cyclopenta-1,3-diene makes it volatile and easily vaporizable.
Cyclopentadiene Melting Point
Cyclopenta-1,3-diene does not have a well-defined melting point due to its tendency to polymerize at lower temperatures. However, it can exist in a frozen or solid state at very low temperatures. The presence of impurities or dimerization can affect the observed melting behavior.
Cyclopentadiene Density g/mL
The density of cyclopenta-1,3-diene is approximately 0.77 g/mL. Density is a measure of mass per unit volume and indicates how tightly packed the molecules are within a substance. The relatively low density of cyclopenta-1,3-diene suggests that it is less dense than water and can float on its surface.
Cyclopentadiene Molecular Weight
The molecular weight of cyclopenta-1,3-diene is approximately 66.10 g/mol. It is calculated by summing the atomic weights of all the atoms in the molecule. The molecular weight provides important information about the compound’s mass and is used in various calculations and conversions in chemistry.
Cyclopentadiene Structure
Cyclopenta-1,3-diene has a cyclic structure consisting of a five-membered carbon ring with alternating single and double bonds. The molecule adopts a planar conformation due to its aromaticity and exhibits electron delocalization within the ring system. This unique structure contributes to the reactivity and properties of cyclopenta-1,3-diene.
Cyclopentadiene Solubility
Cyclopenta-1,3-diene is sparingly soluble in water, but it dissolves readily in many organic solvents, such as benzene and ether. Its solubility characteristics are influenced by the polarity of the solvent and the ability of the solute molecules to interact with the solvent molecules. The solubility behavior of cyclopenta-1,3-diene is important in various applications involving organic synthesis and chemical reactions.
| Appearance | Colorless |
| Specific Gravity | 0.77 |
| Color | N/A |
| Odor | Pungent |
| Molar Mass | 66.10 g/mol |
| Density | 0.77 g/mL |
| Melting Point | N/A |
| Boiling Point | 41.5 °C |
| Flash Point | -12 °C |
| Water Solubility | Insoluble |
| Solubility | Soluble in organic solvents (benzene, ether) |
| Vapour Pressure | 110 mmHg at 25 °C |
| Vapour Density | 2.3 (air = 1) |
| pKa | N/A |
| pH | Neutral |
Cyclopentadiene Safety and Hazards
Cyclopenta-1,3-diene poses several safety hazards that need to be considered. It is highly flammable and can form explosive mixtures with air. The compound has a low flash point of -12 °C, which increases the risk of fire. It is also harmful if swallowed, inhaled, or absorbed through the skin, and can cause irritation to the eyes, skin, and respiratory system. Cyclopentadiene may undergo polymerization, leading to the release of heat and pressure. It is important to handle this chemical with caution, using appropriate protective measures, such as wearing gloves, goggles, and respiratory protection. Proper storage, handling, and disposal procedures should be followed to minimize risks.
| Hazard Symbols | Flammable |
| Safety Description | Keep away from heat, sparks, and open flames. Use in a well-ventilated area. Wear protective gloves and eyewear. Avoid inhalation or skin contact. |
| UN IDs | UN 2044 |
| HS Code | 29021900 |
| Hazard Class | 3 (Flammable liquid) |
| Packing Group | II |
| Toxicity | Harmful if swallowed, inhaled, or absorbed through the skin. Can cause irritation. Proper precautions should be taken during handling. |
Cyclopentadiene Synthesis Methods
Various methods allow for the synthesis of cyclopenta-1,3-diene.
One common approach to synthesizing cyclopenta-1,3-diene involves the dimerization of butadiene. In this method, transition metal complexes such as nickel or cobalt catalyze a [4+2] cycloaddition reaction between two molecules of butadiene, resulting in the formation of cyclopenta-1,3-diene.
Subjecting cyclopentanone, a cyclic ketone, to high temperatures in the presence of an acid catalyst enables its thermal decomposition reaction, resulting in the formation of cyclopenta-1,3-diene. This reaction yields cyclopenta-1,3-diene as one of the products.
The dehydrogenation of cyclopentene, an unsaturated hydrocarbon, provides another method for synthesizing cyclopenta-1,3-diene. This process involves the use of catalysts such as platinum or palladium to facilitate the removal of two hydrogen atoms from cyclopentene, resulting in the formation of cyclopenta-1,3-diene.
By exposing dicyclopentdiene, a dimeric compound, to high temperatures, the retro-Diels-Alder reaction occurs, leading to the synthesis of cyclopenta-1,3-diene. This thermal process induces a reverse [4+2] cycloaddition reaction, leading to the production of cyclopenta-1,3-diene.
These synthesis methods provide different routes for obtaining cyclopenta-1,3-diene, allowing researchers and chemists to choose the most suitable approach based on their specific requirements and available resources.
Cyclopentadiene Uses
Cyclopenta-1,3-diene finds application in various fields due to its versatile properties. Here are some common uses of cyclopenta-1,3-diene:
- Cyclopenta-1,3-diene plays a crucial role in various fields as it possesses versatile properties. It serves as a valuable building block in organic synthesis, enabling the production of numerous compounds, including pharmaceuticals, polymers, and specialty chemicals.
- The Diels-Alder reaction extensively utilizes cyclopenta-1,3-diene, as it acts as a diene component and facilitates the construction of complex ring structures in organic chemistry. This reaction enables the formation of fused ring systems.
- In polymer production, cyclopenta-1,3-diene acts as a monomer and contributes to the manufacturing of synthetic rubbers and elastomers. It plays a vital role in developing materials with desirable mechanical properties.
- Cyclopenta-1,3-diene finds application in the formulation of adhesives and coatings due to its reactivity and ability to undergo cross-linking reactions. It enhances the adhesion and durability of these products, making them suitable for various applications.
- Fuel additives, such as methylcyclopentadienyl manganese tricarbonyl (MMT), utilize cyclopenta-1,3-diene derivatives to improve combustion efficiency and reduce engine knock in gasoline.
- Cyclopenta-1,3-diene plays a significant role in aromaticity studies as it exhibits aromatic characteristics with its cyclic structure. Researchers employ it as a model compound to understand and investigate aromatic systems.
Questions:
Q: What does cyclopentadiene dimerize?
A: Cyclopenta-1,3-diene can undergo dimerization, where two molecules of cyclopentadiene combine to form a dimer called dicyclopentadiene.
Q: Is cyclopentadiene aromatic?
A: Yes, cyclopenta-1,3-diene is considered aromatic due to its planar structure and the presence of a conjugated system of alternating single and double bonds.
Q: Why is 1,3-cyclopentadiene (pKa = 16) a much stronger acid than cyclopentane (pKa = 44)?
A: 1,3-cyclopentadiene is more acidic than cyclopentane because it has a conjugated system of pi electrons, which stabilizes the resulting negative charge upon deprotonation, making it easier to lose a hydrogen ion.
Q: Which of the following would react fastest with 1,3-cyclopentadiene?
A: Compounds with electrophilic double bonds, such as maleic anhydride or aldehydes, would react faster with 1,3-cyclopentadiene due to the nucleophilic nature of cyclopentadiene.
Q: Why does cyclopentadiene crack?
A: Cyclopentadiene can undergo cracking, a process where it undergoes thermal decomposition, often resulting in the formation of smaller fragments or polymerization, due to its inherent reactivity and tendency to undergo rearrangements.
Q: pKa of cyclopentadiene?
A: The pKa of cyclopenta-1,3-diene is approximately 16.
Q: Cyclopentadiene monomer?
A: Cyclopenta-1,3-diene exists primarily as a monomer, but it can dimerize under certain conditions to form dicyclopentadiene.
Q: Reaction of cyclopentadiene with maleic anhydride?
A: Cyclopenta-1,3-diene undergoes a Diels-Alder reaction with maleic anhydride to form the adduct cyclopentadiene-maleic anhydride, a common synthetic route for the production of various compounds.