Dehydrogenation of primary alcohols. Catalytic dehydrogenation of alcohols
(ORGANIC CHEMISTRY)
Water cleaner from alcohols (dehydration):
Sour reagents are used as dehydration catalysts: sulfur and phosphoric acid, aluminum oxide, etc. The order of cleavage is most often determined by the Rule Zaitseva (1875): when water is the formation of water, hydrogen is most easily cleaved from the neighboring the least hydrogenated carbon atom ...(ORGANIC CHEMISTRY)
Oxidation of alcohols
Alcohols are oxidized easier than hydrocarbons, and, and first of all, carbon is subjected to oxidation, at which the hydroxyl group is located. The most suitable oxidizing agent in the laboratory is a chromium mixture. In industry - air oxygen in the presence of catalysts. Primary...(ORGANIC CHEMISTRY)
Oxidation of ethyl alcohol to acetic acid.
Ethyl alcohol is oxidized to acetic acid under the influence of acetic acid bacteria Gluconobacter and Acetobacter. These are gram-negative chemorganoometerotrophic, non-disposition, rowing organisms, movable or motionless. Acetic acid bacteria of these clans differ in each other ...(Basics of Microbiology)
Catalytic dehydrogenation of paraffins
An important industrial method is also catalytic dehydrogenation of paraffins over chromium oxide: most of the laboratory methods for producing olefins are based on the reactions of cleavage (elimination) of various reagents: water, halogen or halogen breeds from the respective derivatives of the limit ...(ORGANIC CHEMISTRY)
Alcohol dehydrogenation reactions are necessary to obtain aldehydes and ketones. Ketones are obtained from secondary alcohols, and aldehydes from primary alcohols. Catalysts in processes are copper, silver, copper chromites, zinc oxide, etc. It is worth noting that compared with the copper catalysts of zinc oxide is more persistent and does not lose activity during the process, but it can provoke the dehydration reaction. In the general form, the dehydrogenation reaction of alcohols can be presented as follows:
In industry, alcohol dehydrogenation is obtained by compounds such as acetaldehyde, acetone, methyl ethyl ketone and cyclohexanone. The processes proceed in the current of the water vapor. The most common processes are:
1. It is carried out on a copper or silver catalyst at a temperature of 200 - 400 ° C and atmospheric pressure. The catalyst is a carrier Al 2 O 3, SNO 2 or carbon fiber, which is applied to the components of silver or copper. This reaction is one of the components of the vacuer process, which is an industrial method for producing acetic aldehyde from ethanol by dehydrogenation or oxygen oxidation.
2. It may proceed in different ways, depending on the structural formula of its starting material. 2-propanol, which is a secondary alcohol dehydrated to acetone, and 1-propanol, being primary alcohol, dehydrated to propane at atmospheric pressure and process temperature 250 - 450 ° C.
3. It also depends on the structure of the initial compound, which affects the final product (aldehyde or ketone).
4. Methanol dehydrogenation. This process is not fully studied, but most researchers identifies it as a promising process of formaldehyde synthesis, not containing water. Different parameters of the process are proposed: The temperature is 600 - 900 ° C, the active component of the catalyst of zinc or copper, the carrier of silicon oxide, the possibility of initiating the reaction of hydrogen peroxide, etc. At the moment, most of the formaldehyde in the world is obtained by oxidation of methanol.
The generally accepted mechanism of the dehydration of alcohols is the following (for simplicity, ethyl alcohol is taken as an example):
The alcohol joins the hydrogen ion stage (1) to form a protonized alcohol, which dissociates stage (2), giving a water molecule and the carbonia ion; Then the ion of carbonia stage (3) loses hydrogen ion and alkene is formed.
Thus, the double bond is formed in two stages: the loss of the hydroxyl group in the form of [Stage (2)] and the loss of hydrogen (stage (3)). This is distinguished by this reaction from the dehydrogalogeneration reaction, where the cleavage of hydrogen and halogen occurs simultaneously.
The first stage represents the acid-base equilibrium according to Brenstec - Loury (Section 1.19). When sulfuric acid dissolves in water, for example, the following reaction occurs:
The hydrogen ion has moved from a very weak base to a stronger base with the formation of an oxonium ion. The main properties of both compounds are due, of course, a vapor pair of electrons that can bind the hydrogen ion. The alcohol also contains an oxygen atom with a different pair of electrons and its basicity is comparable to the basicity of water. The first stage of the proposed mechanism can be most likely to submit as follows:
The hydrogen ion switched from the bisulfat ion to a stronger base (ethyl alcohol) with the formation of a substituted oxony ion of protonated alcohol.
Similarly, stage (3) is not pushing the free ion of hydrogen, but its transition to the strongest of the existing grounds, namely
For convenience, this process is often depicted as joining or cleavage of hydrogen ion, but it should be understood that in all cases there is actually a proton transfer from one base to another.
All three reactions are given as equilibrium, since each stage is reversible; As will be shown below, the reverse reaction is the formation of alcohol alcohols (sec. 6.10). Equilibrium (1) is shifted very much to the right; It is known that sulfuric acid is almost completely ionized in alcohol solution. Since the concentration of carbonium ions available at each moment is very small, equilibrium (2) is shifted to the left. At some point, one of these few carbonium ions reacts by equation (3) to form alkenes. In dehydration, the volatile alkene is usually distilled off from the reaction mixture, and thus the balance (3) shifts to the right. As a result, the entire reaction comes to the end.
The carbonium ion is formed as a result of the dissociation of protonized alcohol; At the same time, the charged particle is separated from
the neutral particle is obvious, this process requires significantly less energy than the formation of carbonium ion from the alcohol itself, since in this case it is necessary to tear off the positive particle from the negative. In the first case, the weak base (water) is cleaved from the carbononium ion (Lewis acid) is much easier than a very strong base, hydroxyl ion, i.e. water is the best outgoing group than hydroxyl ion. It is shown that the hydroxyl-ion is almost never cleaving from alcohol; The response of splitting in alcohol in almost all cases require acid catalyst, the role of which, as in the present case, is the protonation of alcohol.
Finally, it should be understood that the dissociation of protonized alcohol becomes possible only due to the solvation of carbonium ion (CP. Section 5.14). The energy for breaking the bondage of carbon - oxygen is taken due to the formation of a large number of ion-dipole bonds between the carbonia ion and the polar solvent.
Carbonium ion can enter various reactions; Which one occurs, depends on the experimental conditions. All the reactions of carbonium ions are eclipsed equally: they acquire a pair of electrons to fill an octet in a positively charged carbon atom. In this case, the hydrogen ion is cleaved from the carbon atom, adjacent to the carbon atom of a positively charged depleted electrons; A pair of electrons, previously engaged in connection with this hydrogen, can now form -EB
This mechanism explains acid catalysis during dehydration. Does this mechanism also explain the fact that the ease of dehydration of alcohols decreases in a series of tertiary secondary primary? Before answering this question, it is necessary to find out how the stability of carbonium ions changes.
Hydration alkenes The most important industrial importance is the hydration of olefins. Attaching water to olefins can be carried out in the presence of sulfuric acid - sulk acid hydration or when the mixture of olefin with water vapor over the phosphate catalyst H3P04 on aluminosilicate ...(ORGANIC CHEMISTRY)
Oxidation of alcohols
With alcohol burning, carbon dioxide and water are formed: under the action of conventional oxidizing agents - chromium mixture, permangat potassium oxidation is primarily a carbon atom at which the hydroxyl group is located. Primary Alcohols are given when the aldehyde is oxidized, which are easily moving ...(ORGANIC CHEMISTRY)
Oxidation of ethyl alcohol to acetic acid.
Ethyl alcohol is oxidized to acetic acid under the influence of acetic acid bacteria Gluconobacter and Acetobacter. These are gram-negative chemorganoometerotrophic, non-disposition, rowing organisms, movable or motionless. Acetic acid bacteria of these clans differ in each other ...(Basics of Microbiology)
Catalytic dehydrogenation of alcohols
The conversion of alcohols in aldehydes and ketones can also be carried out by dehydrogenation - transmission of alcohol vapor over a heated catalyst - copper or silver at 300 ° C: the interaction of alcohols with magnesium organic compounds (Grignar reagents) leads to the formation of limit hydrocarbons: this ...(ORGANIC CHEMISTRY)
Alcohol and alcohol-containing products
It includes only ethyl alcohol (raw and rectified alcohol), regardless of the type of raw materials, from which it is manufactured (food or non-tech). Technical alcohol (this is not ethyl) is not an excise product, it is obtained from wood or petroleum products. For the production of excise ...(Taxation of commercial activities)
