Pyridine, 5-chloro-2-fluoro-4-iodo-

5-Bromo-2-pentene-4-alkynenyl halogenated compounds. It has the following chemical properties:
1. ** Nucleophilic Substitution Reaction **: The halogen atom has high bromine activity and is vulnerable to attack by nucleophilic reagents. If co-heated with an aqueous solution of sodium hydroxide, the hydroxyl nucleophilic reagent will replace the bromine atom to generate 5-hydroxy-2-pentene-4-yne. Because the electronegativity of the bromine atom is greater than that of the carbon atom, the carbon-bromine bond electron cloud is biased towards the bromine, causing the carbon atom to be partially positively charged and vulnerable to attack by the nucleophilic reagent.
2. ** Addition reaction **:
- ** Addition to halogen **: The carbon-carbon double bond and the carbon-carbon triple bond in the molecule are both electron-rich and have high reactivity. Taking bromine as an example, it can be added to 5-bromo-2-pentene-4-alkyne. When the amount of bromine is small, it is preferentially added to the double bond, because the activity of the double bond is slightly higher than that of the triple bond, to form a dibromo substitute; when the amount of bromine is excessive, both the double bond and the triple bond can be added, and more bromogens are added.
- ** Addition to hydrogen halide **: Following the Markov rule, hydrogen atoms in the hydrogen halide are added to the unsaturated carbon atoms containing more hydrogen. If added with hydrogen chloride, the hydrogen atom is added to the carbon with more hydrogen in the double bond or triple bond, and the chlorine atom is added to the other unsaturated carbon.
3. ** Oxidation reaction **:
- ** oxidized by potassium permanganate **: The carbon-carbon double bond and triple bond will be oxidized and broken in the case of strong oxidants such as acidic potassium permanganate solution. The double bond is generally oxidized to form carboxylic acid or carbon dioxide (depending on the structure), and the tribond oxidation can produce carboxylic acid, carbon dioxide or ketone (depending on the specific structure). 5-Bromo-2-pentene-4-alkyne in the case of acidic potassium permanganate solution, the double bond and the triple bond will be oxidized. The product varies depending on the specific reaction conditions and the degree of oxidation.
- ** Catalytic oxidation **: Under appropriate catalysts and specific conditions, carbon-carbon double bonds can be selectively oxidized to alcaldes or ketones.
4. ** Polymerization **: There are unsaturated bonds in the molecule. In theory, polymerization can occur under initiators or specific conditions. Double or triple bonds are opened and connected to each other to form a polymer. However, the actual reaction needs to consider specific conditions and reactivity.

5-Bromo-2-pentene-4-alkyne is an important intermediate in organic synthesis. The common synthesis methods are as follows:
1. ** Nucleophilic substitution reaction with halogenated hydrocarbons as raw materials **:
- Select suitable halogenated hydrocarbons, such as the reaction of brominated halogenated hydrocarbons with nucleophiles containing alkynyl and alkenyl groups. For example, 1-bromo-3-chloropropane reacts with lithium acetynyl at low temperatures and in an anhydrous and oxygen-free environment. The negatively charged ethynyl nucleophilic in lithium acetylide attacks the carbon atom connected to bromine in 1-bromo-3-chloropropane, and the bromine ion leaves to form an intermediate containing alkynyl and alkyl groups. This intermediate reacts with the alkenyl Grignard reagent. The negatively charged carbon nucleophilic in the Grignard reagent attacks the carbon atom connected to chlorine in the intermediate, and the chloride ion leaves, and through a series of reactions, 5-bromo-2-pentene-4-yne is obtained.
- The reaction conditions are strict, and the reaction conditions are anhydrous and oxygen-free to avoid the reaction of nucleophilic reagents with water and oxygen; low temperature controls the reaction rate and selectivity to prevent side reactions, such as the self-coupling of nucleoph
2. ** Through the addition reaction of alkynes **:
- Addition of alkynes containing alkenyl groups as substrates with brominating reagents. Such as 1-pentene-4-alkynes and hydrogen bromide are added under the action of a suitable catalyst. The catalyst can be selected from peroxide. In the presence of peroxide, hydrogen bromide and 1-pentene-4-alkynes undergo anti-martensitic addition. Bromine atoms are added to double-bonded carbon atoms containing more hydrogen, and hydrogen atoms are added to double-bonded carbon atoms containing less hydrogen, thereby obtaining the target product 5-bromo-2-pentene-4-alkynes. < Br > - Pay attention to the amount of catalyst and the reaction temperature. If there is too little catalyst, the reaction rate is slow; if there is too much, other side reactions may be triggered. If the temperature is too high, the selectivity of the addition reaction will be reduced, and side reactions such as polybromide may occur.
3. ** Transition metal-catalyzed coupling reaction **:
- The coupling of alkenyl halides, alkynyl halides and bromine-containing reagents is used under the action of transition metal catalysts such as palladium catalysts. Such as alkenyl bromide, alkynyl bromide and zinc bromide react in the presence of palladium catalysts and ligands. The palladium catalyst is first oxidized with the alkenyl bromide to form a palladium intermediate, which is then metallized with the alkynyl bromide, and finally reduced and eliminated, forming a carbon-carbon bond to obtain 5-bromo-2-pentene-4-alkyne.
-Transition metal catalysts and ligand selection are crucial, and different ligands affect catalyst activity and selectivity. At the same time, attention should be paid to the pH and reaction time of the reaction system. Improper pH will affect catalyst activity, and too long or too short time is not conducive to the formation of the target product.

"Tiangong Kaiwu" says: "The genus of hardware is salty and useful." 5-boron, 2-silicon, 4-zirconium-hafnium, the use of these numbers, widely involved in various fields.
Boron, although small but macro. In the field of metallurgy, adding boron to steel can increase its hardness and improve its toughness. Steel has excellent performance, suitable for all kinds of fortifications, building buildings and heavy builders depend on it. And in the making of glass, boron is included in it, which can change its properties, making glass heat-resistant and corrosion-resistant, indispensable for daily and industrial use. In the agricultural mulberry industry, boron is necessary for plants, and appropriate boron supplementation can promote the cultivation of crops and increase the fruit.
Silicon has a wide range of uses. In the world of electronics, silicon is the crystal based on silicon, which is the bone of the chip. Computers and communication devices all use silicon crystals as the core to promote the rapid transmission of information, making the world like a neighbor. In the genus of building materials, silicon is also the key. In cement and ceramics, silicon is the key, making buildings strong and durable, shielding from wind and rain to protect thousands of homes. And in the process of chemical industry, silicon compounds have many wonderful uses, making lubricants and waterproof materials, each developing its own strengths.
Both zirconium and hafnium also have their uses. In the field of nuclear engineering, zirconium has excellent performance, radiation resistance and corrosion resistance, and is an important material for nuclear reactors to ensure the stable use of nuclear energy. Hafnium emits light and heat in the fields of electronics and aerospace, and can adjust its performance and make the operation more stable. In aerospace equipment, it can increase its strength and reduce its weight, and help the equipment to rise to the sky.
Therefore, 5-boron, 2-silicon, and 4-zirconium-hafnium are of great use in many fields such as metallurgy, electronics, building materials, agricultural mulberry, nuclear engineering, and aerospace. They have made great contributions to the progress of the world and the benefit of people's livelihood.

The price of five taels of salt, two taels of oil, and four ingots of sugar cannot be determined between the cities of Guanfu, but the price often changes with various conditions.
The price of salt is necessary for people's livelihood, related to the taste of food and health. The price may change, or due to the weather, the weather is surly, and the salt production is damaged, the price will rise; or the geographical location, the place of origin is far and near, and the transportation is difficult. It can also be caused by personnel, the leniency of decrees, and the manipulation of merchants. The price of five taels of salt, whether high or low, varies from time to time, and cannot be generalized.
As for oil, cooking is also a priority. The fluctuation of its price is related to the harvest of oil. If there is a good year and the oil is sufficient, the price will be stable; if there is a shortage of years and the harvest is meager, the price will rise. And the difficulty of production and the amount of labor are all related to the price. Therefore, the price of two taels of oil is not constant and often varies depending on various things.
And sugar, which is pleasing to people, is also needed in the market. The price of its change depends on the production of raw materials such as sugar cane. If it is properly planted and the raw materials are abundant, the price may be easy; if there is a disaster and the raw materials are scarce, the price will rise. And whether the sugar is refined or not, and the quality can also make the price different. The price of four ingots of sugar is constantly changing, which is difficult to determine.
It is necessary that the market prices of five taels of salt, two taels of oil, and four ingots of sugar change from time to time due to the interaction of various factors such as weather, geographical location, and personnel. If you want to know the exact value, you can only obtain it if you visit it in detail at that time and place.

"Tiangong Kaiwu" states that the five-year-two-alum-four-year-old sand is quite exquisite in its storage conditions.

The white sand is dry and should be placed in a dry, cool and ventilated place. Because it is easy to deliquescent, if the storage environment is humid, it is easy to turn into juice and lose its effect. The storage place should be protected from water and humidity, not near rivers and lakes, nor in low-lying places. It needs to be sealed with pottery urns, porcelain jars, etc., one is to prevent it from absorbing moisture, and the other is to prevent it from being in excessive contact with the outside air to avoid qualitative changes.
Alum substances, such as alum, green alum, etc., also need a dry environment. Although alum is relatively stable, it is also afraid of moisture, and it is easy to agglomerate when damp, which affects its use. Green alum is even more, not only afraid of moisture, but also sensitive to light. Under light, green alum is prone to oxidation reaction, and the color gradually changes, and the effectiveness is also reduced. Therefore, alum storage should be protected from light, filled in dark clay pots or wooden boxes, and then placed in a dry and ventilated place before long-term storage.

Class of things, many toxic and corrosive. When storing, it must be isolated from other things, especially not mixed with food, medicinal materials, etc., to prevent accidental ingestion or contamination. The storage place should be guarded by special personnel, with obvious warning signs to prevent inadvertent contact, causing danger. And it needs to be checked regularly. If there is any damage to the packaging or change in material properties, it should be dealt with in time to ensure the safety of storage.
In this way, the five-year-old two-alum and four-year-old sand can be properly stored without losing its properties for emergencies.