3-Bromo-4-fluoropyridine

3 Rivers and 4 Desecration, its main users are related to the order of heaven and earth, the harmony of yin and yang, and the relationship between people's livelihood.
Since ancient times, the ancestors of Huaxia have respected the heaven and the earth, and worshiped the mountains and rivers. The "Shangshu · Shundian" states: "Looking at the mountains and rivers, it is all over the gods." The river is the flow of water, its galloping momentum, and its moisturizing power are immeasurable. The desecration, the river, the river, Huai, and the economy, are the veins of the rivers, connecting the four seas, and are related to the water conservancy and transportation of the world.
The use of river desecration is first in irrigation. Farming in ancient times depended entirely on water conservancy. The Yellow River and the Yangtze River, the mother rivers of China, nourish the fertile fields on both sides of the river, so that the millet is abundant and the people can eat. "Water and drought come from people, and they don't know hunger." Dujiangyan diverts the water of the Minjiang River to irrigate the western Sichuan plain, creating a "country of abundance". This is the work of river blasphemy irrigation.
The second time in the boat. The river is a natural waterway, goods can be circulated, and business travel is endless. In the spring and autumn, Wu State opened the Hangou to communicate with the Jianghuai River and promote economic exchanges between the north and the south. The Grand Canal in the Sui Dynasty connected the five major river systems of the Haihe River, the Huaihe River, the Yangtze River, and the Qiantang River, strengthening the political, economic, and cultural ties between the north and the south. "The world turns into a canal, and it depends on this canal." It can be seen that the river Water vapor evaporates in the river, forming clouds and causing rain, regulating the regional climate. And the wetlands around the river provide habitat for many creatures and maintain ecological balance.
And the river is also important in sacrificial ceremonies. The Son of Heaven sacrificed the famous mountains and rivers in the world, and the princes sacrificed the mountains and rivers in his territory. The god of river blasphemy is revered by all the people, in order to smooth the weather and maintain the peace of the country. This is the way the ancestors feared nature and prayed for harmony between heaven and earth.
In short, the three rivers and four blasphemies, irrigating farmland, relieving the boat, regulating the climate, and maintaining etiquette are of paramount use to the national economy and people's livelihood, and harmony between heaven and earth.

There are many methods for the synthesis of 3-bromo-4-hydroxypyridine, which are described in detail as follows:
First, pyridine is used as the starting material. First, pyridine is brominated, and liquid bromine can be used under appropriate catalyst such as iron powder under heating conditions to obtain bromopyridine. This step requires attention to the reaction temperature and the amount of bromine to prevent the formation of polybrominated products. Subsequently, bromopyridine is hydroxylated. Usually, a strong base such as sodium hydroxide in an aqueous solution is reacted at high pressure to replace the bromine atom with a hydroxyl group to obtain 3-bromo-4-hydroxypyridine. However, the conditions of this method are more demanding, high temperature and high pressure require high equipment, and there may be many side reactions.
Second, use suitable substituted benzene as the raw material. First construct the pyridine ring, for example, through a multi-step reaction, the substituted benzene is converted into a pyridine derivative. This process often involves reactions such as condensation and cyclization. Some specific reagents can be used, such as nitrogen-containing compounds and carbonyl-containing compounds, under appropriate conditions to form a pyridine ring. After that, the pyridine ring is modified by bromination and hydroxylation. The advantage of this route is that the position and type of substituents on the pyridine ring can be flexibly designed, but the steps are cumbersome and the total yield may be limited.
Third, biosynthesis is used. Some microorganisms or enzymes have specific catalytic ability to catalyze specific substrates to generate 3-bromo-4-hydroxypyridine. This method has the advantages of green and environmental protection, mild reaction conditions and high selectivity. However, it is difficult to find suitable microorganisms or enzymes, and the cost of cultivating microorganisms or extracting enzymes is high, so large-scale production still needs to solve many technical problems.
Fourth, halogenated pyridine derivatives are used as raw materials. If suitable halogenated pyridine derivatives can be obtained, halogen atoms at specific positions can be replaced with hydroxyl groups through selective substitution reaction. This method requires the selection of suitable nucleophilic reagents and reaction conditions to ensure the selectivity of the reaction and minimize the occurrence of side reactions in other positions.

The position of measuring the weight of objects in ancient times, and its materiality is unique.

, is the smallest of the ancient weight positions. "1. The Law": "One can hold two thousand millet, and it weighs twelve." This shows that the weight of one grain is determined by the weight of a certain amount of millet, and it is one in twenty-four. The special feature of this is that it is used to measure the weight of things, such as rare materials, small goods, etc. Because the weight it represents is small, it is especially important to measure a small number of items.
And, in terms of relative terms, it represents the position of large weight. It played an important role in the ancient system of weights and measures, and was often used in daily transactions and the measurement of goods. For example, food, cloth and other items on the market were measured by weight, which was convenient for the transaction party to calculate the value. The formulation of weights also has a grid, and other weights are interacted with each other to form a complete weight measurement system.
From a physical perspective, the weights represented by 3 - and 4 - are different, reflecting the ancient people's ability to quantify the weight of goods. It is not the weight of the goods, but also contains various information such as ancient society, technology and culture. Under the level of ancient science and technology, it was possible to formulate such a precise weight measurement level, which developed the pursuit of the ancient people's precise physical quantity, and played an important role in promoting the development of ancient commercial work, manual work and other fields, and also laid the foundation for the development of the world's measurement system.

In today's world, in the market, there are three or four degrees, and their value can be investigated.
Since they have been in the world, their weight and thickness, and the value of their shape, are all different. Three degrees, in the early days of martial arts, are as important as their text, but they will not be long ago. Because of the,
Up to the fourth century, also in history. In the life of Emperor Wen of the Song Dynasty in the Southern Dynasty, the fourth century. Its methods of cultivation and martial arts are not limited, but there are also private disadvantages. The value of the fourth century is also multi-terminal. First, the longer the age, the rarer the existence of the world, the higher the price; second, the method of writing and writing, the exquisite method, everyone is good, and the water is also high; third, consider the place where it was made. Different places have different workmanship, materials or differences, and the value is also different.
Generally speaking, the value of the third and fourth centuries is not uniform in today's city. It is necessary to test the quality of the product, version, age, law, place and other factors. Collectors in the spring world are all sensitive to their hearts, and they can only get their fairness if they are not good. City people's transactions are also based on this. Don't be confused by it, and don't sell it.

The sentence in English: #3 - #4 - #3 - #4 - #3 - #4 - #3 - #3 - #3 - #4 - #3 - #3 - #4 - #3 - #3 - #3 - #3 - #4 - #3 - #3 - #3 - #3 - #4 - #3 - #3 - #3 - #3 - #4 - #3 - #3 - #4 - #3 - #3 - #3 - #3 - #3 - #3 - #3 - #3 - #3 - #3 - #3 - #3 - #3 - #3 - #4 - #3 - #3 - #3 - #3 - #3 - #3 - #3 - #3 - #3 - #3 - #3 - #3 - #3 - #3 - #3 - #3 - #3 - #4 - #4 - #3 - #3 - #3 - #4 - #4 - #4 - #4 - #4 If there is a channel, the water is easy to leak, not only the water source, but also the efficiency of the impact. Furthermore, the speed of water flow also needs to be considered, and the channel is easy to drain. The narrow and short channel of the channel is reasonable, so as to achieve the best effect.
In addition, it is also necessary to consider the change of the season. In the dry season, there is less water, so it is appropriate to flow to ensure safety; in the rainy season, there is a lot of water, so be careful to prevent flooding, and make water in advance. And the way of the road, or if there is a need for others to take it, it is important to balance and distribute it reasonably, so that it can be used, and it cannot be biased.
In addition, 3-4-4-4-4-4-4-4-4-4-4-4-4-4-4-4-4-4-4-4-4-4-4-15-15-15, the matter is of great importance, and it is necessary to be careful in order to benefit the water conservancy and the people.