4-f-pyridine

In "Tiangong Kaiwu", the main uses of finless porpoise are as follows:
One of them is edible. Finless porpoise meat can be regarded as food. In the past, in some places bordering rivers and lakes, materials were relatively scarce, and people would use finless porpoise as a food source. However, finless porpoise meat is coarse, the taste is not excellent, and the fishy smell is heavy, so it is not a widely popular delicacy.
Second, finless porpoise skin has certain uses. Its skin is tough and can be used to make some small leather goods, such as wallets, scabbards, etc. After special tanning treatment, finless porpoise skin can have certain durability and meet the needs of some daily small objects.
Third, finless porpoise also has unique significance in traditional fishing culture. In the fishing activities of the Yangtze River Basin, the finless porpoise is regarded as a "omen" by fishermen. When the finless porpoise appears frequently and is more active, some fishermen will think that it is a sign that the weather, hydrology and other conditions are about to change, so as to arrange subsequent fishing activities. For example, if the finless porpoise is very active, it may indicate that the river water will rise and fall in the near future, and fishermen will prepare in advance, strengthen the boat, organize the fishing gear, etc.
But it should be made clear that with the development of the times, the finless porpoise has now become a national first-class protected animal, and its use has been strictly prohibited, in order to better protect this rare species and maintain ecological balance.

The nature of rivers is both rigid and soft, with thousands of changes, and contains many physical characteristics.
Its strength, the momentum of water, is unstoppable. When encountering high mountains and mountains, the torrent pours out, like thousands of troops galloping. "The rocks pierce through the air, the waves hit the shore, rolling up thousands of piles of snow." Under this scene, the stiffness of the water is fully evident, capable of breaking down boulders, chipping away cliffs, and its strength is huge, it can move mountains and fill valleys. When the flow of water is rapid, energy converges, like a sharp blade, cutting deep canyons on the earth, such as the Three Gorges of the Yangtze River, which is carved by the river with the strength of the river over the years.
However, it also has a soft state. Where the flow is slow, the water waves are not active, gentle. Water can give shape to things, and when it meets a square, it is round when it meets a circle, and there is no shape. "The spring is silent and cherishes the trickle, and the shade of the tree shines on the water and loves the sunshine and softness." The trickle moisturizes all things, quietly nourishes the earth. The softness of water lies in its tolerance, which can accommodate all things in it, allowing fish and shrimp to grow, and aquatic plants to grow, creating a place for life in the world.
Furthermore, water is fluid. It never stops, from high to low, galloping endlessly. "How much sorrow can I ask you? It is like a river of spring water flowing east." The flow of water symbolizes the rhythm of life, and it is also like the passage of time, which is irreversible. Because of the flow, it can gather into rivers, rush into the sea, and complete the cycle of nature.
And the water has buoyancy. "As if you are walking along a reed, you are at a loss." Boats and boats travel on the water, relying on the buoyancy of water, they can travel smoothly. This buoyancy allows aquatic creatures to swim freely without spending too much energy to fight gravity.
It is also soluble. The water of rivers can dissolve everything. Minerals, nutrients, etc. are dissolved in water, transferring substances and energy to the ecosystem, maintaining the balance and development of the entire river ecology.
The physical characteristics of rivers, the combination of rigidity and softness, flow, float, dissolve, and intertwine, together draw the wonderful water scene of this world, and deduce a unique chapter between heaven and earth.

4-Bromopyridine is a key intermediate in organic synthesis, and its synthesis methods are diverse. The following are the common ones:
1. ** Direct bromination method **: Pyridine is used as the starting material, and under appropriate reaction conditions, the bromination reaction is carried out with brominating reagents such as liquid bromine and N-bromosuccinimide (NBS). This method is relatively direct, but the activity of hydrogen atoms at different positions on the pyridine ring varies, and the selectivity of the reaction needs to be properly controlled. If liquid bromine is used, it is usually catalyzed by Lewis acid (such as FeBr 🥰) and reacted in a suitable solvent (such as dichloromethane). The reaction mechanism is roughly that the bromine molecule is polarized under the action of Lewis acid to generate active bromine positive ions, which then attack the pyridine ring and generate 4-bromopyridine through electrophilic substitution reaction. However, this method is prone to produce by-products, such as isomers such as 2-bromopyridine, and the separation and purification are slightly more complicated.
2. ** Metal catalytic coupling method **: This is a commonly used strategy for constructing carbon-bromine bonds. First, the halogenated compounds of pyridine derivatives (such as 4-chloropyridine) can be used to metallize with metal-organic reagents (such as organolithium reagents, organomagnesium reagents, etc.), and then interact with brominating reagents to achieve the introduction of bromine atoms. Second, transition metal-catalyzed coupling reactions are also widely used. Taking palladium catalysis as an example, 4-pyridyl boronic acid reacts with brominated reagents in a suitable solvent (such as toluene/water mixed solvent) in the presence of palladium catalysts (such as Pd (PPh)) and bases (such as potassium carbonate). This method has high selectivity and can effectively avoid substitution in other positions. The product has good purity, but the catalyst price is relatively high, the reaction conditions are more stringent, and an anhydrous and oxygen-free environment is required.
3. ** Pyridine Derivative Conversion Method **: Pyridine derivatives with convertible functional groups are first prepared, and then the functional groups are converted into bromine atoms through a specific reaction. For example, 4-pyridyl methanol can be first converted into 4-pyridyl carboxylic acid by oxidation reaction, and then reacted with a brominating agent (such as phosphorus tribromide) to realize the conversion of carboxyl groups to bromine atoms, thereby obtaining 4-bromopyridine. This pathway has a little more steps, but the characteristics of different functional groups can be used to precisely regulate the reaction to achieve higher selectivity and yield.

In order to keep the water flowing smoothly, many things should be paid attention to when storing and transporting it.
As far as storage is concerned, the first location should be selected. It is necessary to find a high and dry place to prevent water from being polluted or lost due to rainwater. If a water storage pool is built underground, the wall of the pool must be reinforced to prevent leakage. And the material of the pool should be clean and harmless, and it should not chemically react with the water to maintain the purity of the water. Regularly clean the water storage tank to remove its debris, algae, etc., to maintain the cleanliness of the water.
As for transportation, the choice of channels is very critical. If water is transported by pipeline, it is necessary to check the material of the pipeline. Although the metal pipe is strong, it is easy to rust and corrode, which affects the water quality; the plastic pipe is light and resistant to corrosion, but it may be deformed and leaked under high temperature. Therefore, according to the characteristics of the water and environmental conditions, choose it carefully. When laying the pipeline, ensure that the slope is appropriate, help the water flow, and reduce energy consumption. And the pipeline connection must be tight to prevent dripping.
If water is carried in a ditch, it needs to be dredged frequently. Because the water flow is prone to carry sediment and debris, it accumulates at the bottom of the canal and causes the water flow to be blocked. Also strengthen the dike to prevent collapse. Along the water delivery line, set up monitoring points to measure the water quality and flow in real time. If there is any abnormality, quickly check the cause and deal with it.
During the transportation Through factories, farmland and other areas, take protective measures to avoid industrial wastewater, pesticides and fertilizers, etc. In this way, the water can be stored and transported in good condition and move freely.

The finless porpoise is also a spiritual object in the river. Its market price is very difficult to determine.
The finless porpoise is a rare genus, and it is a national-level protection of living beings. It is forbidden to buy and sell, so it can be judged by ordinary prices. In the past, when the ecology was not damaged, the finless porpoise swam leisurely in Jiangchuan, and its value was more than money. At that time, the existence of the finless porpoise was a sign of ecological balance in the river, and it coexisted and prospered with all kinds of aquariums. Its wonders in nature are like poetry, and it can't be weighed with gold and silver.
However, since the past few years, human affairs have disturbed the habitat of the finless porpoise. The construction of hydraulic engineering, the multiplicity of ships, and the discharge of sewage have caused their habitats to gradually frown, and the number has dropped sharply. Although it is priceless in the city, its endangered state makes our generation well aware that it is precious and beyond usual. In terms of value, saving the finless porpoise requires incalculable financial and material resources. This is all due to carelessness in the past, which caused ecological damage. If we want to remedy it now, we need to pour a lot of effort.
The finless porpoise is precious, not the gold and silver in the city can be measured, but the gift of heaven and earth creation and the symbol of natural harmony. We should do our best to protect it and make the finless porpoise swim again in the blue wave. This is the responsibility of thousands of generations. It is not the price of money. It is the weight of ecological sustainability.