Ether is a product in which hydrogen is a hydroxyl group of alcohol or phenol is substituted with a Hydrocarbon Group. The general formula is RO-R’, and R and R’ may be the same or different. The same is called a Simple Ether or Symmetric Ether. what’s ether uses?
The different ones are called mixed ethers. If R, R’ are respectively a carbon atom at both ends of an organic group, it is called a cyclic ether such as ethylene oxide.
Most ethers are colorless liquids at room temperature, have an aroma, have a low boiling point, are lighter than water, and are stable in nature. Ethers generally have an anesthetic effect. For example, ether is a commonly used inhalation anesthetic in clinical practice.
Structure and Chemical Bond
The structural formula of the ether is ROR (R’), Ar-OR or Ar-O-Ar (Ar’) (R = Hydrocarbon group, Ar = Aromatic Hydrocarbon Group). The ether has a bond angle of about 110° and a CO bond length of 140 pm. The energy of the rotational energy barrier of the CO bond is small, and the oxygen-binding ability of water, Alcohol and Ether molecules is similar. According to the valence bond theory, the hybrid state of the oxygen atom is SP3.
The electronegativity of the oxygen atom is stronger than that of carbon, so the alpha hydrogen atom attached to the oxygen is more acidic than the carbon-linked alpha hydrogen atom, but its acidity is not comparable to the carbonyl alpha hydrogen atom.
The common Nomenclature of ethers is to add the word “ether” after the hydrocarbon group. The “two” word of the symmetrical ether can be omitted. The order of two different groups of ethers is usually: a small group followed by a large group.
The naming convention of aromatic ethers is: Phenyl or aromatic hydrocarbons are in the front. English naming is in alphabetical order. The crown ether is named x-crown-y, x represents the total number of atoms in the ring, and y represents the number of oxygen atoms in the ring.
Classification of Ethers
The two ethers of the same hydrocarbon group become symmetrical ethers, also called simple ethers. An ether with two different hydrocarbyl groups is called an asymmetric ether, also called a mixed ether.
According to the class of two hydrocarbyl groups, ethers can also be classified into fatty ethers and aromatic ethers.
In a fatty ether, ether in a molecule which is not bonded by an oxygen atom and a carbon atom to a cyclic ether structure is called an acyclic ether. It can also be subdivided into saturated ethers and unsaturated ethers.
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An ether in which an oxygen atom and a carbon atom are combined to form a cyclic ether structure is called a Cyclic Ether. The oxygenated ether on the ring is referred to as an internal ether or an epoxy compound. A macrocyclic ether containing a plurality of oxygens is called a crown ether.
Physical properties of Ether
Cyclic ethers such as tetrahydrofuran and 1,4-dioxane are miscible with water because of the oxygen atoms of such ether molecules are more exposed to molecules than alkyl ethers (chain ethers), so The polarity is greater than the latter. ether uses
Most ethers are volatile, flammable liquids. Unlike alcohols, hydrogen bonds cannot form between ether molecules, so the boiling point is much lower than the boiling point of the same component of alcohol.
For example, the boiling point of ethanol is 78.4°C, the boiling point of methyl ether is -24.9 °C, the boiling point of n-butanol is 117.8. At °C, the boiling point of diethyl ether was 34.6 °C. The boiling points of commonly used ethers are shown in the table below.
Most ethers are insoluble in water, but the commonly used tetrahydrofuran and 1,4-dioxane are completely miscible with water because they form hydrogen bonds with water.
Although the number of carbon-oxygen atoms of diethyl ether is the same as that of tetrahydrofuran, the oxygen and carbon framework of the latter form a ring together, the oxygen atom protrudes out, and hydrogen bonds are easily formed with water, and the oxygen atom in the ether is “enclosed” in the molecule.
In the middle, it is difficult to form hydrogen bonds with water, so ether can only be slightly soluble in water. At room temperature, 1% to 1.5% of water is soluble in the ether; 7.5% of the ether is soluble in the water.
Since the two dissolve little together, and most of the organic matter is easily soluble in ether, it is usually used to extract various substances which are easily soluble in ether from water, but the ether extract contains a small amount of water, which needs to be dried before the ether is distilled. Water, meanwhile, also loses a portion of the ether during the extraction process. ether uses
Ether is a commonly used solvent in the laboratory, and the salt compound is insoluble therein, so that diethyl ether is added to the salt solution of the compound to precipitate a precipitate-salt compound. Ether is extremely volatile and catches fire. The ether gas and air form an explosive mixture. An electric spark will cause a violent explosion.
Ether is an anesthetic commonly used in surgery, and its action is not chemical but is a physiological change caused by dissolution in nerve tissue fat. This anesthetic effect is determined by the partition coefficient of the ether in the fatty phase and the aqueous phase. ether uses
Vinyl ether is also an anesthetic. Its anesthetic performance is 7 times stronger than that of ether, and it is extremely fast, but it quickly reaches the risk of too deep anesthesia, thus limiting its practical application in this area.
Chemical properties of Ether
1 Automatic Oxidation
If diethyl ether and other ethers in constant contact with air or with light can generate less volatile peroxide (peroxide).
Most auto-oxidation is carried out by a free radical mechanism.
Peroxide ether is an extremely explosive polymer. When the ether containing the compound is distilled, the ether peroxide remains in the container and will explode if heated. In order to avoid accidents, it should be checked before using ether or other ethers with longer storage time, such as tetrahydrofuran.
If peroxide is added, adding an equal volume of 2% potassium iodide acetic acid solution will release iodine and make the starch solution purple. Or blue. A solution of ferrous sulfate prepared from trivalent iron sulfate and 50% sulfuric acid is added to about 1/5 of the volume and violently oscillates to destroy the peroxide.
The peroxide can also be reduced with lithium aluminum hydride or the like. In order to prevent the formation of peroxide, 0.05 μg/g of sodium diethylaminothioformate was added to the commercially available anhydrous ether as an antioxidant. ether uses
Even if the ether does not contain peroxide, since the ether is highly volatile and its vapor is flammable, there is often a risk of explosion and fire. Be sure to take precautions when using it.
2 The Formation of Strontium Sheep Salt
The ether can form a secondary strontium salt as a base and concentrated sulfuric acid, hydrogen chloride or a Lewis acid (such as boron trifluoride) due to a lone pair of electrons on the oxygen atom.
Ethyl ether can absorb a considerable amount of hydrochloric acid, gas to form a strontium salt. If it is put together with an organic base such as an amine in diethyl ether, the amine hydrochloride can be precipitated, which is a method for preparing an amine salt. ether uses
For example, by reacting an ether with a secondary salt formed of boron trifluoride and a fluoroalkane, a tertiary sulfonium salt can also be formed.
3 Carbon-Oxygen bond Cleavage Reaction
The ether is heated together with hydriodic acid, and the carbon-oxygen bond is broken. The cleavage is the formation of strontium salt by acid and ether, and then the SNl or SN2 reaction occurs depending on the nature of the alkyl group.
In the SN2 reaction, the tertiary alkyl group is susceptible to the SN1 reaction to form an iodoalkane and alcohol, and in the presence of an excess of the acid, the alcohol produced is also converted to an alkyl iodide.
The above reaction can also be carried out with hydrobromic acid and hydrochloric acid, but since neither of them is active in hydroiodic acid, concentrated acid and a relatively high reaction temperature is required.
For mixed ethers, the order of carbon-oxygen bond cleavage is: tertiary alkyl > secondary alkyl > primary alkyl > aryl.
The aryl group is conjugated to the lone pair of oxygen and has some double bond properties and is therefore difficult to break. Zeisel S’s methoxy (-OCH3) quantitative measurement is based on the above reaction. Natural complex organic molecules often contain methoxy groups.
A certain amount of the compound and an excess of hydriodic acid with a methoxy group-containing heat, the generated methyl iodide was distilled into silver nitrate in alcohol solution, and referred to in accordance with the generated silver iodide content can be calculated of the original molecule Methoxy content.
The cyclic ether reacts with the acid to open the cyclic ether to form a dihaloalkane when the halogenated alkyd is in excess.
The asymmetric cyclic ether is ring-opened to form a mixture of the two products. ether uses
When hydrochloric acid is reacted with tetrahydrofuran, it needs to be added, and anhydrous zinc chloride forms 1,4-dichlorobutane in the presence of excess acid, which is an important intermediate material for making nylon.
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4 Ring-opening reaction of 4,1,2-epoxy compounds
A typical ether is a relatively stable compound and is often used as a solvent. The ether is very stable to the base, for example, the ether does not react with the aqueous solution of sodium hydroxide, the alcohol the solution of sodium alkoxide, and the liquid ammonia solution of sodium amide.
However, compounds such as ethylene oxide are completely different from general ethers. They not only react with acids but also have mild and rapid reaction conditions and can react with different bases.
The reason is that its three-membered ring structure makes the orbits of the atoms not fully overlapped in front, but is connected to each other by a bending bond. Due to this relationship, there is a tension in the molecule, which is easy to react with various reagents, and the ring is opened. It is very useful in organic synthesis, through which a variety of compounds can be synthesized.
5 Acid-catalyzed Ring-Opening Reaction
The ring-opening reaction is carried out according to SN1 or SN2 history with SN1 characteristics. Acidic open loop, open loop direction: generate stable carbon cation
The ring-opening reaction of diborane with epoxide is also acid-catalyzed ring-opening, diborane can be regarded as a dimer of borane, and the outer layer of boron is in an electronic configuration, which can be complexed with oxygen in the epoxide. Its action is similar to protonic acid, so the negative hydrogen in the borane is transferred to the ring carbon atom with more substituents.
6 Alkaline Ring-Opening Reaction
The base-catalyzed ring-opening is mainly active reagent, strong nucleophilic ability, and there is no positive or negative charge on the epoxy compound. This is a SN2 reaction, the C-O bond is broken and the bond between the nucleophilic reagent and the ring carbon atom. The formation proceeds almost simultaneously when the reagents are selected to attack the ring carbon atoms with fewer substituents because the carbon has less steric hindrance. ether uses
The alcohol can be prepared by dehydration reaction:
2 R-OH → ROR + H2O (at high temperature)
The reaction process requires high temperatures (typically at 125 ° C). The reaction also requires acid catalysis (usually sulfuric acid). The above method is effective for the preparation of symmetrical ethers, but does not work for asymmetric ethers, such as diethyl ether is readily prepared by this method and cyclic ethers can also be prepared by this method (intramolecular dehydration). In addition, this method will introduce certain by-products, such as intramolecular dehydration products:
R-CH2-CH2(OH) → R-CH=CH2 + H2O
In addition, this method can only synthesize some simple ethers, which is not suitable for complex molecular ether molecules. For complex molecules, milder conditions are needed to synthesize. ether uses
Williamson ether synthesis
Nucleophilic substitution reaction of halogenated hydrocarbons and alkoxides: R-ONa + R’-X → ROR’ + NaX
This reaction is called: Williamson synthesis. The reaction is carried out by treating the alcohol with a strong base to form an alkoxide and then reacting with a hydrocarbon molecule bearing a suitable leaving group.
The leaving group herein includes a halogen such as iodine or bromine, or a sulfonate. This method is generally not applicable to aromatic halogenated hydrocarbons (eg, bromobenzene, see Ullmann condensation). The method is also limited to the first-order halogenated hydrocarbon to obtain a better yield and is not suitable for the secondary halogenated hydrocarbon and the tertiary halogenated hydrocarbon because it is too easy to generate the E2 elimination product.
In a similar reaction, the alkylhalohydrocarbon can also undergo a nucleophilic substitution reaction with a phenolic anion. Although RX cannot react with alcohol, phenol can carry out the reaction (phenolic acid is much higher than alcohol), and it can be reacted by a strong base such as sodium hydride to form phenol anion. The phenol can replace the X leaving group in the halogenated hydrocarbon to form a phenol ether structure, which is the SN2 mechanism.
C6H5OH + OH- → C6H5-O- + H2O
C6H5-O- + RX → C6H5OR
Ullmann diaryl ether synthesis
The reaction of Ullmann diaryl ether synthesis is very similar to the Williamson reaction, except that the substrate is an aromatic halogenated hydrocarbon. This reaction requires a catalyst to be carried out, such as copper.
Electrophilic addition reaction of alcohol to olefin
The alcohol can be electrophilically added to the activated olefin:
R2C=CR2+ R-OH → R2CH-C(-OR)-R2
The reaction requires acid catalysis. Mercury trifluoroacetate (Hg(OCOCF3)2) is often used as a catalyst for this reaction, and the reaction produces a solid with Vladimir Vasilyevich Markovnikov. Chemical ethers. Using similar reaction conditions, tetra hydropyranyl ether (THP) acts as a protecting group for the alcohol.
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After years of research and experimentation, scientists oxidized methanol to ethers, dimethoxymethane, and incorporated this liquid substance into gasoline to mix a high-efficiency ether-based clean gasoline, dimethoxymethane gasoline.
In November 2011, the State Intellectual Property Office issued a licensing notice for the patented technology of dimethoxymethane gasoline.
Methoxymethane gasoline not only has high power performance but also costs 700 to 1,000 yuan per ton lower than conventional gasoline. This type of gasoline does not cause damage to the car’s engine and even has a protective effect. At present, dimethoxymethane gasoline is favored by many gas stations. ether uses
Dimethyl Ether Fuel
There are three main applications of dimethyl ether fuel on diesel engines.
1. Pilot method
Dimethyl ether was first introduced into the diesel engine cylinder to improve the ignition performance of the diesel engine when it was used to burn methanol. There are many introduction schemes, and there is a typical TOR (Torch Ignition Chamber) scheme.
Considering the high certain number and self-ignitability of dimethyl ether, a small amount of dimethyl ether enters the ignition chamber as a fire promoter at the initial stage of the intake stroke or compression stroke, and burns first in the late stage of the compression stroke to make the temperature inside the cylinder Elevation, which promotes the ignition of the main fuel, and also has some impact on the performance and emissions of the diesel engine.
The introduction of dimethyl ether significantly improved the cold start performance of the diesel engine.
2. Direct combustion method.
The diesel engine directly burns in the cylinder with liquid dimethyl ether as a fuel. However, the current dimethyl ether special jet pump technology is still immature, and it cannot solve the lubrication problem and leakage problem of the high-pressure oil pump plunger pair and the injector needle pair caused by the low liquid viscosity of dimethyl ether. Therefore, this method is more difficult. ether uses
3. The mixed combustion method of dimethyl ether and diesel.
When this method directly mixes dimethyl ether and diesel fuel as diesel fuel, the diesel fuel supply system needs to maintain a high working pressure and at the same time, the diesel engine operates at a higher temperature. The key to this method is the precise control of the blending ratio of dimethyl ether to diesel blended fuel.
At this stage of the ether, the mixed combustion method is mainly applied to the diesel engine. Ether is extremely volatile, highly flammable and has a high oxygen content. It can improve the combustion of mixed fuels and reduce emissions when mixed with diesel.