Автор: Melar
Practical use for ethers
Burn it The first four alcohol functional groups methanol, ethanol, propanol, butanol can be biologically synthesized to be used as an alternative to fossil fuels as they burn very cleanly, producing only CO2 and water. Since it is relatively safe and nontoxic, it can be used to dissolve many organic compounds which are otherwise insoluble in water. It is used, for example, as a solvent in medical drugs, perfumes, and vegetable essences. Cleaning with it methylated spirits is a product of ethanol mixed with a small quantity of methanol or isopropyl alcohol, which can be used to clean industrial machinery.
Ethanol can be used as an antibacterial to sterilize the skin before injections and is commonly used in hand sanitizers. Ethers Solvent Ethers are quite unreactive and therefore are desirable solvents for fats, oils, waxes, perfumes, resins, dyes, gums, and hydrocarbons.
In addition, vapors of certain ethers are used as insecticides and fumigants for topsoil. Nitroglycerin, Nitrogen Monoxide in Medicine Sedative Ethers also play an important role in pharmacology and medicine, especially for use of anesthetics.
Methoxymethane or otherwise known as codeine is an effective pain-relieving drug and is the primary ingredient in morphine. The pKa values of some macrocyclic analogues of crown ether 4 were previously determined [ 20 ].
Thus, the observed spectral changes in acidic conditions were probably caused by solvatochromic effects. This assumption is consistent with the fact that the photophysical properties of acridine derivatives are generally extremely sensitive even to small polarity changes of the medium [ 21 ]. In the case of fluorescence titration, a slight decrease in the intensity of emission was observed, which can also be attributed to solvatochromic effects see part c and d in Fig. However, partial protonation of host 4 cannot be totally excluded based on the results.
The 9-hydroxyacridine tautomeric form of complexed host molecule 4 contains an acridine-like nitrogen atom, which shows a weakly basic character [ 15 ]. In contrast, additions of 0. It suggests that the tautomeric equilibrium of the heteroaromatic unit shifts toward the acridone form due to the protonation of the 9-hydroxyacridine tautomer.
At the end point of the titration after addition of 40 eq acid the spectrum returned to that of a similar one of free acridono-macrocycle 4 see part c of Fig. The same titration procedure was also carried out using fluorescence spectroscopy Fig. Trends in the series of spectra changed direction after the addition of 0. The spectra obtained from the titration of the free macrocycle with nitric acid are shown in Fig.
The spectral change as a function of the amount of the added acid was significantly greater in the case of acridino-macrocycle 3 than that for acridono-crown ether 4. It suggests that the crown ether stabilized by substitution at position 9 in its acridine form is more sensitive to acidic medium due to its increased basicity compared to the acridone form. The resulted spectrum is shown in Fig. In the case of fluorescence measurements the results see part c and d in Fig.
It also suggests that the protonation of the acridino-crown ethers is less effected by the complexation than that of the acridono-analogues. Changes in the pK a of protonated macrocycles upon complex formation As it was mentioned earlier, the nitrogen atom of acridono-crown ethers is not basic.
In the case of these macrocycles, complexation induces tautomerism of the heterocyclic unit, which has been previously confirmed by IR- and 1 H-NMR spectroscopies and single-crystal X-ray diffraction [ 16 , 17 ]. These studies - in accordance with the present work - support that the 9-hydroxyacridine tautomeric form is preferred during the complex formation.
Theoretically, the pKa of the protonated acridono-crown ether complex could be determined by the protonation of the basic nitrogen of its 9-hydroxyacridine tautomeric form 5. However, based on this study it is assumed that the heteroaromatic unit is converted back to its tautomeric acridone form upon protonation, which inhibits complex formation.
Hence, the pKa for this complex equilibrium system cannot be determined spectroscopically due to the copresence of the acridone tautomeric form. The fitted curves for crown ether 3 and its complex are shown in Fig. It can be seen that the pKa of the protonated macrocycle decreased by approximately one unit as a result of complex formation. In the case when the lone pair of the nitrogen atom of the host molecule is involved in the coordination with the guest molecule, the basicity of the heteroatom decreases.
The change in the pKa value also shows that protonation and complex formation are in a competitive relationship with each other. In more acidic conditions, protonation of the nitrogen of the crown ethers caused deviance in the response of the sensors. Detection was carried out in aqueous medium in all cases, in which the conjugate acid of the parent acridine has a pKa of 5. Thus, for acridono-crown ethers, complexation would not inhibit protonation and vice versa.
However, it is only a presumption. This competition can manifest via the shifting of the tautomerization equilibrium and the decreasing electron donating ability of nitrogen upon the coordination of metal ions. Thus, the pH-range for application could only be extended to about 6. Since this limit was 4. As mentioned previously, it is not possible to determine the pKa of the protonated hydroxyacridine tautomer of acridono-crown ethers 5 based on spectrophotometry.
The magnitude of the decrease in pKa values upon complexation for acridono-macrocycles can be estimated as 2 units based on the above considerations and previous studies on these types of sensor molecules [ 22 , 23 ]. Results are shown in Fig. All these prove that the host molecule forms a more stable complex in the absence of acid. In order to quantify the stability of the complexes global nonlinear regression method was similarly used to determine stability constants based on spectroscopic titration data.
Results show that in acidic conditions, the logarithm of the complex stability constant is less by 1. This can be attributed to shifting the tautomeric equilibrium toward the acridone form in acidic conditions, which tautomer of the heterocyclic unit is unfavorable for complex formation.
Stability constants were also determined for crown ether 3 containing an acridine unit in the same conditions. This can be attributed to the possibility of tautomerism. The inhibitory effect of protonation could be reduced by tautomerization. Studies showed that only the acridine form of the heterocyclic unit took part in the complexation with the metal ion. However, in the cases of both crown ethers host molecules 4 and 3 a high competition took place between protonation and complex formation.
It also indicates the key role of the nitrogen atom among the other donor atoms of the macrocycle in molecular recognition. Conclusions Comparison of the reported types of sensor molecules was carried out using hosts 3 and 4 as model compounds, which are suitable candidates for general studies on factors influencing practical applications. Therefore, in the case of the acridono-macrocycles, complexation is less sensitive to acid and the pH-sensitivity of the crown ethers decreases even more after complexation.
There is a weak competition in this case. The pKa of the protonated acridino-crown ether 3 changes only half as much upon complex formation than it does of the hydroxyacridine tautomer 5 of acridono-crown ethers 4. There is a strong competition. Therefore, in terms of pH-sensitivity, crown ethers containing an acridone unit are more advantageous.
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Cleaning with it methylated spirits is a product of ethanol mixed with a small quantity of methanol or isopropyl alcohol, which can be used to clean industrial machinery. Ethanol can be used as an antibacterial to sterilize the skin before injections and is commonly used in hand sanitizers. Ethers Solvent Ethers are quite unreactive and therefore are desirable solvents for fats, oils, waxes, perfumes, resins, dyes, gums, and hydrocarbons. In addition, vapors of certain ethers are used as insecticides and fumigants for topsoil.
Benefits of Space Exploration to Mankind Sedative Ethers also play an important role in pharmacology and medicine, especially for use of anesthetics. Methoxymethane or otherwise known as codeine is an effective pain-relieving drug and is the primary ingredient in morphine.
Ethyl Ether or just ether was one of the first anesthetics used for surgical procedures during the s. However, ether is highly flammable and has been mostly replaced by other less-flammable anesthetics, such as nitrous oxide and halothane. Industrial Purposes Ethoxyethane ethyl ether is quite volatile and therefore used as a starter fluid for diesel engines and gasoline engines in cold weather.
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